Gotta look at the cards with higher CUDA core counts. Pick your budget, then get the card with the most CUDA cores within that budget. If it were me, I would look at the GTX 460, even one of the cut down, cheap models with less RAM and less bandwidth, like the SE version or the 768 MB version.
By the way, I think it's great that you qualified your question. Without a doubt when someone asks about a PhysX card, there's always people coming on and giving their opinions as to why having dedicated PhysX is a bad idea. If you do it properly and use it in demanding PhysX games like Batman, you'll see a nice impovement, maybe as much as 25% better framerates.