GameFire for Windows
I love playing WoW, but with my aging computer getting a decent frame rate is dang near impossible. One of my guild mates suggested GameFire to squeeze out a few extra FPS and since I was bouncing between 14~20 FPS on the lowest graphics setting I thought I was considering it. Then a random dungeon instance that would have made Leeroy Jenkins proud sealed the deal.
GameFire has the Game Advisor that has some suggested system tweaks that will help fine tune your machine in gaming mode. When you want to play a game it allows you to easily switch into Gaming Mode that will apply all your selected tweaks and you are ready to go. Perhaps my results are not typical, but now I am averaging 50 FPS on with graphics on the Good setting where before the refresh rate was unbearable.
If you are looking for a bit of an edge, I would definitely suggest checking it out.