My absolute favourite right now is
www.babyhopesclothdiapers.com She has EXCELLENT customer service, and the best part is that she has free shipping on everything, regardless of the size of your order. Every time I order I get a personal hand written thank you letter from her, along with a gift. She is fantastic.
In the past I have also ordered from
www.naturalbabies.com,
www.abbyslane.com,
www.nickisdiapers.com all with great customer service and great success. These are stores that I always cross check to see where I can get the best deal.
If you're shopping for prefolds, I highly recommend
www.greenmountaindiapers.com. She may not be the cheapest BUT her prefolds are superior to any other. Seriously. People told me this when I was shopping and I was kinda like "yea right" but now that I have some from her, I can definitely notice a difference. Worth every penny.