If you are considering flashing why not do a 9700Pro since you could probably get that for under $50.
This 9700pro on ebay looks exactly like the one in the
Mac Elite wiki.
But if you want to save a few dollars you could get
this 9500pro. As for other card types any other 9500 I would steer clear of, the Pro's are much faster. Though the 9600pro/xt's are nice it is difficult to find on ebay used most all are new in box and overpriced. Most 9700's would be good. For slightly more than the price of the 9700 Pro you can get a 9800Pro/XT at 256MB or for $30-40 you can get a 128mb 9800 SE/Pro.
Note: The 9800 SE get about the same performance as a 9600Pro.
Take a look at the
Mac Elite buying guide.
Whatever card you get make sure it has the 4 BGA RAM chips (they are square) it does not matter where so much where they are shaped just as long as they are not the rectangular ones.
View attachment 111609
Do not get cards with double the RAM chips or the slower rectangular chips
View attachment 111613
View attachment 111614
All pictures are from the Mac Elite website.