Upgrade From Radeon 3850 to What: Upgrade Help

I'm building a new rig and I have everything down except the GPU and I'm afraid my budget is too low. I would like to keep the price as close as possible to 100 USD if at all possible. I like to pretend I'm pretty knowledgeable about computers but I'm just not as familiar with video cards as I am other components. Can any one help me out? 

I have an ATI Radeon HD 3850 IceQ3 from HIS.
http://www.hisdigital.com/us/product2-358.shtml
It's the TurboX (pre overclocked) one so the engine clocks at 735 MHz and the memory clocks at 1.96 GHz. I'm using a 1680x1050s screen and I do a lot of gaming.
 
Here is the Mobo and CPU that I'll be upgrading to because I thought it was relevant: 
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...