Here are some contests I found:

• The Fifth Underhanded C Contest – the scope is to write benign looking code which would pass trough a code-review (and/or there is plausible deniability for the coder), but which does some evil things. Found it via slashdot. Some of the previous solutions are truly ingenious.
• From the Forensics Contest comes Ann’s AppleTV, where you can win … Ann’s AppleTV of course!
• Forensic Practical Exercise #3 – no prizes, just fun (and it isn’t all that simple either!). If you don’t own encase, you can transform the provided image into a DD style raw image using the Sleuth Kit:

  img_cat.exe -v -i ewf Forensic_Practical_3.E01 > dd.raw

  Just consider that the resulting image will be around 4G (because the thumb drive it imaged was 4G).

Good luck to everyone!

PS. The current Ethical Hacker Challenge is still open until the 11th of January.