SSHD and PJ:M I'll also backup. Both great games with great value. I've also found that I really enjoy Everyday Shooter, and flOw(my first PSN purchase :) ).
If you're into puzzle solving type games, I'd say give Elefunk a try also. It's lemmings-esque but quite entertaining. Also if you have a female in the house she'll be entertained by the cute elephants (and yell at you when you let them fall hehe).