I'd recommend
www.newegg.com for buying cheap computers.
Also, for PC users, things like:
managing startup and running processes
spyware and adware removal
memory optimizing and using a memory optimizer
Registry clean / Registry defrag
Disabling unncessary windows services
Having your computer delete your page file on shutdown
Making hard drive partitions (One for Music, One for Games, One for Windows)
Can
drastically speed up your computer. 2 times, 3 times, 4 times Faster
If you have the technical know-how, you can do alot of this yourself.
One GREAT program, however, for this is Tuneup Utilities 2006.
If u get TU 2006 and run all the optimizers, it's almost like working with a new PC.
I'd highly recommend buying TuneUp 2006 if you don't have the technical know-how to manage your running processes, keep your registry clean, and disable unnecessary programs and services.
http://www.tune-up.com/
For Partitioning, I'd recommend Partition Magic.
http://www.powerquest.com/home_homeoffice/products/system_performance/pm80/index.html
Using both of these programs can make your PC feel like new.