My knowledge is also limited to Nvidia cards.
First of all, are you looking for an AGP or PCI Express card? Despite the fact that PCI Express is newer, more often than not the AGP equivalents are more expensive.
(all mentions of dollars are in USD:)
I just recently got a 7600GT (AGP) which is about the best you can get for AGP from Nvidia. I can say that it's a wonderful card to say the least (and for the price, I paid $180). If you want a PCI Express 7600GT, you can pick one up for about $130.
For you I recommend the 7600GS with 512MB ram. The 7600GT only has 256MB. There are a few versions of the GS with 512MB ram Since you do a lot of video editing and no gaming, more memory is more crucial to you. Check
www.newegg.com they seem to have the best prices.
You can also try
www.tigerdirect.com or
www.outpost.comI would not trust ebay for something like this.