I have personally found the dzone cheatsheet on core java to be really handy in the beginning. However the needs change as we grow and get used to things.
There are a few listed (at the end of the post) in on this java learning resources article too
For the most practical use, in recent past I have found Java API doc to be the best place to cheat code and learn new api. This helps specially when you want to focus on latest version of java.
mkyong - is one my fav places to cheat a lot of code for quick start - http://www.mkyong.com/
And last but not the least, Stackoverflow is king of all small handy code snippets. Just google a stuff you are trying and there is a chance that a page will be top of search results, most of my google search results end at stackoverflow. Many of the common questions are available here - https://stackoverflow.com/questions/tagged/java?sort=frequent