Yeah, Cry02 is a cool and not very expensive mod that actually works.
see:
http://www.cryo2.com/products.asp?m=sc&cid=1
I have seen these on a few cars and even saw a guy on a dyno with it. It added about 10% - 20% on a 100 degree day (pretty common here). The cooler the day the less it helps but for the price it is an intresting mod. Plus it looks like a NOS tank ;-)