The original (no number), 7000, and 9 series Radeons will work in the Beige G3 I think, presumably the same is true for the B&W. The original Radeon is actually said to perform better than the 7000, despite being older, so is probably your best choice as the 9 series Mac cards are expensive and said to have poor compatibility with Mac OS 9. You must get a Mac Edition card, as PC versions of the cards won't work (unless you want to get into flashing them). This does make getting one rather more difficult, as you could probably get an old PC card for free, but the Mac ones are hard to find - I had to pay £20 including shipping for mine.

The Beigey has built-in video, though it's not very compatible with Tiger and would give pretty poor performance anyway, so adding a dedicated PCI video card is crucial on a Beige G3. The B&W comes with a basic PCI video card like the Rage, as I don't think it has have built-in video, which is OK but it would still benefit from something better.