JAMA is considered one of the most impressive general medical journals, followed closely by the New England Journal of Medicine. NEJM's review process isn't quite as rigid, and they occasionally let some bad stuff slip in. Not a lot, just every once in a while something
I've always liked the Annals of Internal Medicine, just because the quality of science they publish is consistently excellent.
Oh. And if you're at a major university, most of them pay for subscriptions to services like Elsevier and Blackwell Synergy, and you can pull everything in these journals off the internet for free, as the university has payed for access to all staff and students. You may have to use software like a VPN that connects your computer to the university network and makes it look like it's an internal computer - most of these services check to see where your computer is before granting you access, or use a system like ATHENS.