One of my new favorite shows to watch is In Plain Sight. I spend more of my time watching shows on USA now than anything else. Anyway, if you watch In Plain Sight you know the character Mary Shannon is famous for her sarcasm and witty remarks. In addition to the Wisecrack generator on the USA network site I found this list of sarcastic remarks.
Internerd -Sarcasm - StumbleUpon
I find it's always a good idea to memorize a few so you can whip them out at the right moment. It's good to indulge your inner Mary Shannon on occasion.