The most site i've used is Virwox.com but they charge so much it's unreal. At first i thought hey, it's not so bad... buying SLL with my credit card then BTC with SLL, and in a whim i would have BTC's to any address. But one day i got a little mathematically curious, so i proceeded to check the fees that these guys had. A staggering $40 from $220 they charged me... i was amazed... how could something like this not capture my full attention everytime i would make a charge.

About other sites, i don't know because i haven't used any other. If you plan on using Virwox, mind the fees, they are not small.