I have seen this question asked a few times, so here's the best answer I am able to give.

• I have collected together and added English for some example sentences that demonstrate grammatical points for the HSK 1, HSK 2, and HSK 3. These example sentences can also be downloaded as flashcard files for use in software such as Pleco and StickyStudy.
  
• The excellent AllSet Learning Grammar Wiki has a page that classifies the grammatical points on the site into 6 levels. These seem to correspond roughly to the six HSK levels, so it would be a good idea to ensure you are familiar with the grammatical points in the appropriate levels.
• Another post on this site shows the contents page of the great grammar book Common Chinese Patterns 330 by Qin Xue Herzberg. I have classified the patterns by HSK level, and there are popup tooltips with information about the characters. The best way to use this list is to study the appropriate patterns from the book.
• The sample exams at the official HSK site chinesetest.cn has quite a few sample exams for each level; doing all of the exams is great practice at seeing the different ways grammatical points can occur.
• Some other grammar books that I own that are useful but don't have any information on the HSK level of each point specifically are: Basic Patterns of Chinese Grammar by Chen Ru, Modern Mandarin Chinese Grammar by Claudia Ross, Schaum's Outline of Chinese Grammar by Claudia Ross.
• These sites don't have much information on their suitability for HSK levels, but are a great resources:  Chinese Grammar by Hugh Grigg (who also has an awesome  blog), Oxford University's grammar notes, and these basic review slides at Rutgers are a great way to start.
• The HSK grammar books I have found tend to be focused on the 'Old' HSK, and so they might not match the New HSK too well. I have listed a few in case you are willing to try them (I haven't) Practising HSK Grammar by Zhang Jing, Essentials of HSK Grammar by Zhao Jing, HSK Grammar by Fu Yuping, Brushing Up Your Grammar for HSK by Dong Cui, HSK Grammar Guidebook by Han Zhigang
  
• I would love to find some more good books and resources for studying Chinese grammar- let me know if you have any suggestions

My HSK list browsing script took a step closer to being a real dictionary. I added:

• Pinyin (tones optional) search, no wildcards yet
• English (definition) search
• All of the searches are done from the same edit field, very few things will match both English and pinyin, if they do you'll get 
  
• Greying out of words/chars that only have frequency information and no dictionary entries
• Added pinyin and definitions to the tooltip text for all characters/words.
• Colouring of links to HSK list pages

And it's still lighting fast, and as before shows CC-CEDICT definitions, character composition, and word compounds. Give it a try 现在! http://hskhsk.pythonanywhere.com/cidian?q=%E7%8E%B0%E5%9C%A8

A few people have asked me this by email, so here's the answer I gave them:

• A quick way to get an idea is to look at a description of ability of learners at different HSK levels, and see where you think your level is.
• If you have a list of the vocabulary you know (e.g. flashcards) and would like to know your HSK level you can enter paste your vocabulary into this script: http://hskhsk.pythonanywhere.com/hanzi
• If you don't have a vocab list, the the best to determine your level is to try some of the online or downloadable HSK sample exams from the official website: http://www.chinesetest.cn/
• You can get a rough idea of your level by looking at the vocabulary lists here, click the 'expand definitions' link too see the meanings: http://hskhsk.pythonanywhere.com/hskwords
• There is also an 'HSK Test' here but I have no idea if it works: http://popupchinese.com/hsk/test
• Let me know if there are any other resources out there for finding your HSK level!
  

Remember, to really 'know' an HSK word you have to be able to use it in all of the different ways that Hanban expects you to. See my recent posts on HSK 1, HSK 2, and HSK 3 example sentences.

These HSK 3 example sentences demonstrate the different ways that some HSK 1 words can be used. See my other posts for HSK 1 and HSK 2 example sentences.The first 70 hanzi sentences (to which I added pinyin and English) were taken from the HSK information published by Hanban on www.chinesetest.cn . The rest were created by me to demonstrate the way that specific words (highlighted with 『』square brackets) are used. They are also available as a flashcard text file for HSK levels 1-3. Please share any more examples that you have in the comments. 94 sentences are with hanzi, pinyin, and English are shown after the jump!

These HSK 2 example sentences demonstrate the different ways that some HSK 2 words can be used. See my other posts for HSK 1 and HSK 3 examples. They are taken from the HSK information published by Hanban on www.chinesetest.cn . They are also available as a flashcard text file for HSK levels 1-3. Please share any more examples that you have in the comments. 53 sentences are with hanzi, pinyin, and English are shown after the jump!

These HSK 1 example sentences demonstrate the different ways that some HSK 1 words can be used. See my other posts for HSK 2 and HSK 3 examples. They are taken from the HSK information published by Hanban on www.chinesetest.cn . They are also available as a flashcard text file for HSK levels 1-3. Please share any more examples that you have in the comments. 48 sentences are with hanzi, pinyin, and English are shown after the jump!

The HSK list web pages and mini dictionary that appears when you click on words and characters in the pages have had a quick overhaul. There is a new option at the top of the page to ’expand‘ the characters and words to include frequency, radical, HSK version and definition information for every character displayed.

Thanks Davide for reminding me to give that script some attention!

Give the expanded versions of the pages a try:

HSK Chars: http://hskhsk.pythonanywhere.com/hskchars2012?expand=yes
HSK Words: http://hskhsk.pythonanywhere.com/hskwords2012?expand=yes
Dictionary: http://hskhsk.pythonanywhere.com/cidian?expand=yes&q=%E8%83%BD

As well as learning the vocabulary for each HSK level, you have to learn how to use the words in a sentence. For some words such as nouns this is pretty obvious, but some verbs and other harder to classify words can only really be learned by example. I have created files which give example sentences for HSK levels 1-3, but even if you aren't studying for the HSK they might be useful for you.

You can either browse these files to verify that you understand the usage examples or import them into a flashcard testing app. There are versions formatted for both Pleco and for Hanzi StickyStudy. The formats are simple tab-separated and it shouldn't be hard to modify them for other flashcard programs.  I mentioned this file before, but I have added English translations for level 3, and started adding my own example sentences for a few of the level 3 words where the usage isn't completely obvious.

I've added a dictionary 东西词典 to the script that runs my character analysis tool. It is currently only searchable by Chinese characters, but it has lots of links to related characters and words using character and word composition.  It also shows at a glance information about HSK level and frequency. It contains links to some more polished dictionaries on each character and word. Give it a try here: http://hskhsk.pythonanywhere.com/cidian?q=%E8%83%BD

[Update 2nd December 2013: I added links to an HSK-aware dictionary to all the characters below!]

Once you have learned a few hundred Chinese words, you start to come across sentences where you recognise all of the characters but have no idea what the actual meaning of the sentence is. This is because there are many 'patterns' in Chinese where a set arrangement of words has a specific meaning.

Common Chinese Patterns 330 is a fantastic resource for picking up subtle grammar points that are easily missed. This book will help you to improve your grammar at any level, through clear examples. If you are studying for one of the HSK levels 1-5, you may not want to just work through the book from start to finish however, as you will be introduced to patterns that use characters above your level. The hanzi in the chapter list were coloured by HSK level using this script and then grouped by hand. The colours for HSK levels 1-6 are in the order that they appear in a rainbow: red, orange, yellow, green, blue, violet.

The following list splits up the 'chapter' titles (patterns) by HSK level. Note that many of the patterns will not be encountered at the levels shown even though all of the characters are known at that level. In the long run I don't think it hurts to be exposed to these patterns early on though, and reinforce the meanings of the characters and words that make them up.

Another couple of caveats: The example sentences for each pattern ignore HSK levels of course. It would be a good exercise to create some new example sentences for each pattern that only use characters from the HSK level in which it appears - if I get around to doing this I'll share the results (Feel free to send me any sentences that you create). Also some patterns have alternative words, and the alternatives may have different HSK levels. I have grouped these patterns at the higher of the two levels, to save studying the pattern twice.