Getting close to memory buying time, req. suggestions.

[Peli]

http://pcpartpicker.com/

This is an incredibly helpful website that will help you find the lowest price and watch for trends in prices on computer components. Check it every few days and see what you can pick up.

Edit:

Here's the list of just DDR2-800 RAM sorted by cost per GB (lowest at the top). This'll show you the best bang for your buck.
http://pcpartpicker.com/parts/memory/#s=200800&sort=a6