With a budget of $100, what is the best graphics card I can get?

[12naruto]

I am currently using the Dell Studio Slim Desktop PC, a 1920 x 1080 monitor, and an ATI Radeon HD 4350. I am wondering if there is anything better to upgrade to, I aim to play games like Killing Floor, Blacklight Retribution, L4D, and the newer games coming out without having to play on the lowest settings. Even on the lowest settings, I experience a small deal of frame lag; however, I can play the Call of Duty MW3 and League of Legends on max settings with little trouble.

 

[12naruto]

If you need anymore information, I'll reply ASAP.