Here's a couple of the trading cards you can get:
There's also profile backgrounds, emoticons, and badges you can unlock too. Check out Ty's profile background!
And in case you missed it, a few months ago we updated the game with some new zombie abilities, among other things: https://www.youtube.com/watch?v=AyrYTxbiz9w
Oh and I just uploaded our NSFW trailer on Newgrounds (it was removed from Youtube way back when).