Big shout out for Clifton Cameras. I live about 100 meters away from their shop (no I'm not related, I don't work there blah blah). Solid rep that can be checked online, and they deal in second hand - all from trade ins for people upgrading and updating their kit. They usually have a small but reasonable stock of Nikon/Canon and a good variety of lenses. From having inspected their used stuff the other day (was looking at a few D300) they're all well described (when they say excellent, they mean excellent - and you can see the difference between the way they are graded). More expensive than fleabay obviously, but they've always been great in my dealings with them.
http://www.cliftoncameras.co.uk/Used_Equipment