Building a PC? Check out these tools:

Lifehacker has put together a superb guide that can be found here.

For part lookup and for creating a custom build, try out PCPartPicker.com. They have built a nice little tool that lets you create a custom build and search for all the parts you need or want. They show prices from a large number of online vendors and allow you to get the best bang for your buck.

I am using both of these to build my next PC. I will post a guide when finished.