I have a 9800 gt and $120 i want to upgrade what should I get?

I have a 9800 gt with an amd athlon x2 5200 dual core processor. M2A-VM-HDMI board, 2gb ddr2 6400 win7,750 gb hdd 700w power supply. I want to upgrade my video card, whats the best performance I can get with $120