There are many articles about this topic but I still find in every new one something from where you can learn few things. From this article I would recommend the point 18 talking about how important is the selection of the right AV to keep the good performance of W7. Coincidentally, I have been testing lately Avira AV, the free version, and so far I agree, it's very fast and the impact on W7 performance is very low.
Microsoft Windows 7 is already a much more responsive operating system than its predecessors, but there are tweaks and changes you can make to speed up Windows 7 even more. By reading this list and implementing some of the suggestions, you can increase performance in a very short period of time. If you have any further suggestions on how to improve the speed of a Windows 7 PC, please let us know in the comments section so that we can keep updating this list.