I've had a
Lowepro Micro Trekker 200 for a few years now, and it has held up very well. It is big enough to carry my D2x, 80-200, 28-70, 17-35, 10.5 fisheye, SB-800 flash, plus spare CF cards, batteries, lens cleaning supplies, etc. I beat the crap out of it, and it still protects my gear nicely. However, it is a relatively small backpack, and when you put that much weight in it, it's not exactly what I would call real comfortable to carry all day. It works for me, but I might suggest finding a well stocked camera store, so you can actually try one on and see how well it fits you. I don't think you can go wrong with a Lowepro product, though.