Speaking as someone who just got a lot in,
For memory, I've been going to Coast To Coast Memory (they advertise on Pricewatch). I went to them initially to get a RAM module for my Compaq 486 laptop. They were the only people in the US who had the 24MB RAM module.
Hey, when you've got to do browser testing on a 486 to test out speed of Javascript execution, accept no substitutes.
I actually just got in a large amount of RAM from them this morning also. I have had no problem with them.
For parts, I turn to eBay a lot for specific ones I need, especially the specialized server parts.
I'll also go to Dirt Cheap Drives, since they WILL have parts in stock for darn near anything SCSI made.
However, eBay looks better and better each day
Mitch