This camera bag business is pretty tricky.
Lowepro Nova 1 AW. I bought this first to carry my 400D and kit lens.
After upgrade to 24-105L Nova 1 AW still good for body and L lens (kit lens back in box).
Next wanted to take camera to work and out and about, the Nova 1 looked too much like a camera bag, so I bought a crumpler pretty boy rucksack. I decided on this as it fits body with 24-105L attached and will fit 400D with 70-200 f/4 attached when I eventually get one.
I thought I was done then...... but no!
I bought a 50mm 1.8 that I wanted to use for low light parties / wedding receptions (as guest) so I got a really small Lowepro Rezo Tlz 20 case that just fits the 400D and 50mm attached (will fit 400D + kit lens too)
All set then for every occasion.... oh no!
Rucksack is fine for walks in the country but for sightseeing and city stuff you need a bag where you can quickly retrieve the camera take a shot and put it back out of sight... Enter the Crumpler muffin top 2500. This is a small over shoulder messenger type bag which holds the 400D with either the 24-205 or 10-22 attached. It hangs by my right hand where I can just slip my hand in and pull out the goodies.
I wonder what will be next...