Bitfinex lets you do that, but you have to make a certain minimum deposit to start your account. I think it's about one bitcoin minimum deposit.
You have to verify if you want to withdraw as USD but not if you only withdraw bitcoins. Converting to USD then back to bitcoins is OK without verifying.
Okay thanks, that's worth to look at.
However I've heard that there's been a lot of problems around Bitfinex lately, are there any other alternatives?