Quick plug for a little site that you might find useful if you buy much computer stuff online in the UK. Essentially eSpyer checks the price and stock of items from some of the more popular online computer stores in the UK, a graph is drawn for each item so you can track the prices as they move up and down.
An example of the graph is this one for "AMD (Newcastle) Athlon 64 3800+/2.4ghz L2-512kb 939pin Boxed With 3 Year Warranty" for Ebuyer:
Using the graph you can see the price of the AMD Athlon 64 has dropped a lot recently and use that information to work out when it's likely to be at it's cheapest or perhaps get even cheaper. There's a 'comment' section as well so people can link to reviews of the Athlon 64 3800 to help others work out whether it's worth the money.
One thing I've noticed while using eSpyer is that the price of an item tends to change as it gets re-stocked (generally e-stores seem to reduce the price when a new batch of stock comes in). It's interesting to see how much prices change over a week even.