I bought a 400 MM L series which requires a tripod to use. It was in near-perfect condition, bought used from B&H for about half the new price.
I like B&H. Have been there often (don't go Friday after sundown)! I would like a fixed telephoto or the EF 70-200mm f/2.8L IS II USM Telephoto Zoom Lens. (costs a lot!) I also like the built-in flash, but need to get a nice external one.