Crucial have a tool that when you run it, it suggests the correct memory for you and gives you options based on price and performance.
is there anything similar to this for graphics cards?
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I'm not aware of such a tool. The fundamental difference between memory and graphics cards is that there are far more different types of memory interfaces (DDR1, DDR2, DDR3, and then all the different speeds and timings) than there are graphics ones (which is basically just the question of AGP or PCI-E). The bottom line is, if you have an AGP slot, 99.99% of AGP graphics cards will work in your PC at it's full capacity (assuming the bottleneck isn't somewhere else) - and likewise for PCI-E. This isn't always true for memory as motherboard manufacturers will recommend specific brands and models of memory.
Before going out and buying anything, I'd want to establish that my graphics card is actually the bottleneck. There are tools out there that will let you monitor GPU usage, which is one helpful measure. i.e. If you're playing a game and your CPU usage isn't maxed out** but your GPU usage is, then your graphics card is probably the bottleneck and you'll benefit from a replacement.
** Be careful doing this. Example: If you have a quad-core processor and your game is taking up 25% of the total CPU usage (i.e. 100% of one core) and the game itself doesn't support multiple cores, then your CPU is getting maxed out.
There is no such tool AFAIK, but you can get an list of GPU's arranged based on their memory clock, chipset, price at this site. It helped me a lot.