There are lots of good sites for purchasing medication if you have a prescription. Just make sure they are based in the US (or another reputable country), have a good basis when it comes to business, and that they require you to have a prescription in-hand prior to purchase.
If you don't, I'd be careful. Despite what anyone says, purchasing medication from a website (even if you have a doctor review your application and have a consultation over the phone), it's against the law set forth by the DEA (in the US).
Hope you find your website. Medication online is SOOO much cheaper than a drugstore.