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
I'm a big fan of the AllSet Learning Grammar Wiki, and one of the most useful things I've come across on there is a few pages that list Chinese grammatical points according to their European Common Framework level. These six levels roughly correspond to the six levels of the New HSK, so it would be a good idea for someone studying for the HSK to ensure that they are familiar with all of the grammar points at their level and below. Each list of grammatical points links to a page with more explanations and examples, a really great resource! I have noted the corresponding HSK levels for each page.
[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.

This post won't make much sense on a PC, but it should look fine on a Mac, iPhone, iPad, iPod, and very likely other mobile devices such as some versions of Android (let me know which devices it does and doesn't work on- thanks!). If you install a Unicode font that supports emoticons such as Symbola you will see a few more of the icons and a few less square boxes on a PC.
If you use the pinyin keyboard on an iPhone or iPad you may have noticed that sometimes little Emoji characters) appear amont the matching hanzi. Emoji are the little pictures or icons that were originally created on Japanese phones so that 14 year old girls could make their text messages look cuter.
The following is a list of all of the Emoji that I have notice along with the pinyin needed to type them, and the matching hanzi that the Emoji picture represents. Let me know if you notice any that I have missed.