Well I can tell you what I just went with, but its more than 100$ and is PCIe
I went with the 6800 GS from newegg.com ($209.00 free shipping) and it plays Battlefield 2 on MAX Detail on EVERYTHING @ 1024x768 with no problem, and need for speed most wanted was choppy but playable on my older FX5900 AGP Card. Which is why I upgraded, it was only 128mb where as this PCIe card is 256 and like really fast.
If I was you I would go with one of the 256mb 6600 models, just make sure it has the DDR2 or DDR3 Ram with it, if its the normal DDR DONT BUY IT, I repeat DONT BUY IT. Plain DDR is very slow and doesn't perform when compared to the same card with DDR3 in it!
So they have the 6600GT DDR3 at tigerdirect.com for like 99.95$ or something, really good price, but if you can hold out or dont mind spending a little more get PCIe if you can!
But I have to agree, NFS:MW, is a kick arse game!
my 2 cents