Hi I cant say i have ever used an online pharmacy but i did do some of the development on this website: Welcome To Monarch Pharmacy
and the owner seemed like a pretty good chap.
This isn't a plug as i said i have no experience of ordering from them just that the owner seems quite decent.
It depends on what sort of stuff you're looking to buy. Pharmacy2u.co.uk is a good UK pharmacy site for stuff that you can buy in any high street pharmacy, without a prescription (or any embarrassment!).
If you're referring to prescription-only stuff (benzodiazepines etc.) then there are also some very reliable offshore sites but as the law is unclear on importation, I'm not going to post websites for these on a public forum.
You need to be real careful with online medications, there's a huge amount of fake / counterfeit drugs and toiletries on the market, infact if they can make a profit on it (normally from china) they have probably faked it. Even popular brands of tooth paste have been found.
Oh and they only make it look like the real thing, they chuck the cheapest and nastiest stuff in the ingredient lists, they do not care if it works or not, or if it even kills you.