Retail Sites

RecordedBooks - They make unabridged audio books from many titles (old and new) that you can rent or buy.

CyberGuys - Good site for computer accessories, hardware, etc. Very unique items.

Amazon - A good old standby for variety and price.

TheLEDLight - Unique items with the new LED/flashlight technology.

Smarthome - If you're into home automation, this is one of the big ones.

HarborFreight - Excellent prices on tools. Frequently have free shipping (even for 100 lb + machines).

Sciplus - All sorts of parts, clearance items, that they buy in bulk and sell. Some very bizarre, entertaining items.

BrigadeQuartermasters - Military, camping, outdoors stuff.

ScientificsOnline - Interesting, educational, fun scientific items.

Sportsmansguide - Military, camping, outdoors stuff.

Good Used Book Sites

BottomDollar
MySimon
OnlyOnSale
Bizrate
PriceGrabber
Froogle- These all search multiple companies to give prices on the item you want. Good for competition.

ConsumerReview
RateItAll - These allow you to find out what other people's experiences have been with a particular product or company.

Topozone - United States topo maps online.

Maptech - Map site

Terraserver - Good map site-topos and aerial photos

Mapblast - Map site

ScienceDaily - Science news.

Switchboard - White pages, yellow pages.

PaleoDiet - Excellent introduction to Paleolithic eating. Many links.

Anthropology in the News - One of my favorite sites. Any news that involves anthropology, archaeology, sociology.

NightFury - Site for sales and miscellaneous