I have a Crumpler bag --
http://www.crumplerbags.com/cartInde...g&catId=22 -- and am out of room already. It fits my 10D, 75-300mm, 28-135mm, and 50mm, but *barely*, as in, it's a good thing the bag has a large velcro tab and an extendable strap.
Next lens I buy, I'm going to have to get a new bag. I wish I'd planned ahead, I just wasn't thinking. But the bag itself is great. Looks cool (red, with blue lining, doesn't look immediately like a photo bag, which I like) and is very sturdy. I'll probably buy another Crumpler -- just a bigger one! ;)