Quick Tip: HTML 5 Cheat Sheet
There is a very handy HTML 5 cheat sheet available for download. It's a printable HTML 5 Cheat Sheet that lists all currently supported tags, their descriptions, their attributes and their support in HTML 4. Definitely worth a download and a print!
Please notice that the specification is an ongoing work, and is expected to remain so for many years, although parts of HTML 5 are going to be finished and implemented in browsers before the whole specification reaches final recommendation status.
Link: HTML 5 Cheat Sheet