Hello Tara.
Back in the day - the card to get was the Radeon 7000. The true "mac edition" (a bright green thing) only ever came with 32MB of VRAM. There are a host of these cards selling on Ebay for around $35 US.
Later versions of the Radeon 7000 came with 64MB VRAM (twice as much). You could get "flashed" versions of these cards for the Mac (usually Sapphire or PowerColour brand). If you can, try to get one at the true 183MHz/183MHz speed (as many flashed cards are downclocked). I had a Sapphire card that was quite a decent performer. I once tested it in a G4 Digital Audio against the standard Rage Pro 128 (AGP slot) - and was shocked to find that the Radeon 7000 card in the PCI slot thrashed it by a long shot.
That said, you are only going to get so much performance out of a 33MHz PCI slot. (Unlike later graphics connections such as AGP or PCI-X.) The Radeon 9200 PCI 128MB (which "sinclair" recommended) is a nice card - but probably a bit much. Personally, I wouldn't be spending kind of money on a Beige G3 that has some very serious limitations; such as a 66MHz system bus, and a crippling inbuilt ATA 33MB/sec interface...
As much as I'd like to say that flashing your own card is fun - the reality can be quite the opposite. Mac and PC graphic cards are identical except for the EEPROM on the card. Here the big difference is size. Macs have a 128KB ROM and PC a 64KB ROM. Your success depends on getting a PC card that has a 128KB EEPROM chip. Even then, my experience is that many cards cannot be flashed on a Mac and must be done so on a PC computer. Not to mention the frustrations of flashing blind...
I'd recommend getting a "flashed" 64MB Radeon 7000 off Ebay. Twice as much VRAM is definitely worth it. BUT... do try to get one with a 128KB EEPROM. Some sellers actually remove the existing small 64KB EEPROM and install a larger 128KB one. Otherwise, you'll be getting a flashed PC card with a reduced ROM on it - which can (but not always) lead to instability problems. The reduced ROM's from strangedogs that many use for flashing have a very good reputation. And, at the very least, get one with the latest 226 ROM. Some of the Sapphire cards also come with 5 nano-second VRAM chips (instead of the usual 7ns).
All of these cards will work in both Mac OS 9.2 and Mac OS X. OS X is pretty visual + processor intensive, so a decent graphics card will really help. The Radeon 7000 card also has two video ports - so you can run two monitors with extended display if you want to. And should you ever upgrade to Panther on your Beige G3 use 'XPostFacto' to help install the OS and to make sure the Radeon 7000 is supported. One more thing - if I recall correctly, there is/was a program called "PCI Extreme" that could enhance the graphic cards ability in Panther...
Good luck!
PS - In my opinion, the ultimate card to get would be the original "Radeon Mac Edition PCI". This card was an absolute legend. Although it has only 32MB VRAM - it's much (much) more powerful than the Radeon 7000. See here:
http://www.barefeats.com/gr7000.html
Oh... here you go:
http://cgi.ebay.com/Radeon-Mac-Edit...ryZ25449QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
