The best prices IMHO can be found with step one. Memory is the key to success. Having 512mb on a P3 versus 128mb or 256mb on a P4 I'll take the P3 9 times out of ten.

Step One - Deals!

First you should start reading the "deal" sites. In particular check:
Look at recent or historical deals and try to do better. Things tend to run in cycles and you can count on 10% off from some nearly all the time.

Step Two - Price Engines

If you've picked a specific model from a company that doesn't do their own pure mail-order business check the price search engines. Dell and Gateway for instance do almost all mail order to the end users but most brands like Compaq, IBM, Toshiba and Sony are available from nearly anywhere online. Some good price search engines:

Step Three - Other Shopping Issues

Consider how comfortable you feel about these:

Recent Deals on Laptops

Below are some recent deals I've seen to give some price points. In particular the usual trick is discount coupons, instant rebates and mail-in rebates. These are all pulled from one of the sites in step 1.