There are perfectly reputable parts sources on the internet, but there are shysters too. I know that
www.rockauto.com has a good reputation, as does
www.summitracing, and
www.jegs.com. Beyond that I could only say you should try a small order and see how it goes. I recently ordered $700 worth of stuff from rockauto. It has all arrived, and I am in the process of rebuilding the engine. I am going to order a transmission rebuild kit from an ebay seller called CTpowertrain. They have a very good feedback rating. On ebay you can look at the feeback rating of sellers, and see if you are satisfied with their reputation.
www.jcwhitney.com usually is satisfactory, but they wont have the highest quality. They are consistent in providing their parts though. I have never had a beef with anything I bought from them. The only place you can sometimes beat their prices is on ebay.
One of the nice things about rockauto is that you often get to choose the quality of the part you want - and the price reflects it.
