OK, so right now I'm running the following rig:
AMD Sempron 2500+ (1,75 Ghz)
ASRock K7 Upgrade-880 (well, I'm not sure I remember the exact model right)
1 GB RAM
80 GB HDD
250 GB HDD
DVD +/- R/RW drive
Recently I found that my GPU is somewhat lagging when I try to run some newer games (particularly TR:Legend and HOM&M V). Not so much to be unplayable, but on some occasions it's quite uncomfortable overall.
I've looked through some tests, comparisons and whatnot and it seems that GeForce 6600 GT (GDDR3 variant) seems to be a good choice for increased performance, but I decided it would be better to ask around what you folks think about that choice.
My current R9600 has 128 MB of GDDR1, it seems.
If you have any better ideas for the card to pick for upgrade, please remember that I am constrained by two things:
1. Price. $175 is about the top limit here.
2. AGP. My motherboard is equipped with an AGPx8 slot, so whatever card is suggested must be for that slot.