I have a Tamrac Pro 9 (also called Cyberpack 9) that also holds a laptop in the rear compartment. It is a great bag. All the gear listed in my signature (except the Vivitars) fits in it. [Edit: I have since received a 2nd camera body. I do not carry both in the bag.] There are also several other large compartments in front. I am only showing the main compartment. The bag has a sternum strap and a waist/hip belt to help distribute the weight. I think it weighs about 20 lbs with everything in it.
The Sigma 500 Super flash is shown here, but it covers the nifty fifty.
The 300D camera has a grip on it.
The flash is removed so you can see the nifty fifty
A Sigma 1.4x TC is under the Canon 10-22 lens
In addition to this junk, I also carry lots of batteries, a charger, some CF cards, filters, and so on.