I've been shopping online for more than a decade. Some of my general favorites are Amazon.com and Overstock.com. I like Buy.com and Geeks.com for electronics. For clothing I especially like JCPenney, Sierra Trading Post, Tommy Hilfiger, and Jos. A. Bank. There are dozens of specialty stores also that I regularly shop online as well as big brand favorites like Lowe's, Target, Kohls, and Sears.
I've included links to some of the above stores in the sources section below. I also recommend Shopping-Bargains.com for coupon codes to the above stores (and hundreds more) so you can enjoy free shipping and other great deals.