The 9600 is such a beast, and probably the most expandable Mac ever (Quadra 950 close second). I've found suitable upgrades come up real cheap on eBay from time to time (eg. accelerators, RAM, video cards), if you take your time looking out. Last upgrade for my 9600/350 was the full gamut of RAM (and more!), coming out to under $5 a stick.
A suitable video card is a PC ATI Radeon 7000 (flash it yourself), or I've seen the Mac Edition 9200s kicking around too. Even cheaper, a 3dfx Voodoo 3000 PCI card (again flash it yourself), good for games. A Mac compatible IDE/SATA card is also a must, and any generic PCI USB 1.1 card will probably work fine too. I'd hold out for a G4 accelerator card, the Sonnet ones come up from time to time (I've a 1Ghz G4 in mine which cost ~ $80 a couple of years ago).
JB
A suitable video card is a PC ATI Radeon 7000 (flash it yourself), or I've seen the Mac Edition 9200s kicking around too. Even cheaper, a 3dfx Voodoo 3000 PCI card (again flash it yourself), good for games. A Mac compatible IDE/SATA card is also a must, and any generic PCI USB 1.1 card will probably work fine too. I'd hold out for a G4 accelerator card, the Sonnet ones come up from time to time (I've a 1Ghz G4 in mine which cost ~ $80 a couple of years ago).
JB