I second the recommendation for Dustygroove.com---best online ordering experience I've ever had! I've placed dozens of orders with them over the years, and their website, service, selection and prices are top notch. They keep their online catalog up-to-date seemingly by the minute, and will e-mail you immediately when out-of-stock items on your wantlist come back in stock. When you place an order, it is fulfilled and shipped by the next day. If you're into Funk, Soul, rare grooves, blaxploitation, Jazz, this is *THE* place.
Worst online ordering experience I ever had: www.aquariusrecords.org. One time I spent several hours browsing their catalog and compiling a list of LPs to order. There is *no* online order form and no ability to keep a wantlist. I e-mailed them a list of about a dozen LPs I wanted to order, only to have them send a reply *over a week later* to inform me that most of the LPs I wanted were out of stock, and ask if I wanted to go through with the order. I said no thanks and never tried to place an order with them again. YMMV...