I haven't personally bought anything online through a breeder, but I know there are SEVERAL great breeders out there. You may want to start by looking at the banner ads on this site. The ads you see at the top and the sides of your screen are for breeders who help support this community and this website. I'm sure that you will be safe going to any of them.
Also, it is going to depend on what kind of snake you are looking for. Are you looking for a normal or a morph? Are you looking for something like a pastel or spider, or are you looking for a high end morph? Here are just a couple that I know by reputation that I would recommend...
There are a lot more breeders that I can think of but don't have time to link right now (being at work and all)... Just find a breeder who has the snake you want and I would recommend researching the breeder's rep on the BOI.
I think BHB would be a great site to purchase off of, also 8ballpythons. I think someone already posted up the link for both, so just check out the sites.
I purchased an 08 male normal from Tim and Monica Bailey of Bailey and Bailey Reptiles. I am very happy with my experience that I had with them. Just type Bailey and Bailey reptiles in a search and it will pull up the website. I am very pleased to say that I would purchase from this breeder again.