I have the lowepro orion trekker.
http://www.lowepro.com/Products/Back...n_Trekker.aspx
I can carry my camera, and up to 4 lenses if i had 4! i normally have camera, 3 lenses and the 4th area in the bag i put cable release, spare battery, telescope adapter.. etc.
the top part is great, can put carry wallet/phone/keys etc
handy for going onto planes because you can chuck that on your back, while your carrying other stuff (in my case normally backpack + laptop + handbag!)