You can get a 9800 GT for $79 after MIR on newegg. That is the best card you can get under a hundred dollars in either ATI or Nvidia.
The Nividia GT 240 is intended to replace the 9800 GT at the $90 mark--but is not as fast of a card and costs more.
(The best ATI card you could get would be the single 4830 thats still available on newegg for $94.http://www.newegg.com/Product/Product.aspx?Item=N82E16814161260&cm_re=4830-_-14-161-260-_-Product
The 4670 is a good value card if you prefer the $55-65 price range, but will not perform as well as a 9800gt.
(unless there are some really awesome sales that I have missed)