Well, my graphics card died today and I'm looking to upgrade as far as I can without having my processor bottleneck it. Here's my setup so far.
PSU: 550 Watt with 2 PCI-E connectors
Processor: E6600 Dual Core 2.4 Ghz
Old Graphics Card: 8800 GTS 320 MB (only used one connector, but my computer came with a spare)
RAM: 4 gigs
OS: Windows Vista Ultimate 32 bit
Uh... if I left anything out please let me know. I consulted a friend and he suggested an ATI 4870 512 MB, as he said that was as far as I could go without my processor bottlenecking me.