I’m currently using a Gura Gear Uinta 30L (Previously, it was a Tamrac Adventure 9) backpack. The bottom compartment holds the 1Ds Mark II with attached EF 16-35mm f/2.8 L II lens down the middle. On one side, I have the EF 70-200mm f/2.8 L IS II, on the other, the EF 50mm f/1.4 and a set of Kenko EF extension tubes. In the lid, I keep some small odds and ends such as lens pen, CF reader, spare AA and AAA batteries. The bottom is quite full, but closes properly. The top compartment holds various computer accessories (laptop power adapter, bluetooth headset, usb adapters/charges, serial adapters/cables), a few photo accessories (beanbag, camera remote, flash-bracket bubble-level, Arctic Butterfly 724 spare body and lens caps). I keep the monopod (Giottos MM9780) in the side pocket and loop the handstrap through the handle on the top to hold it steady.
The only gear it won’t currently cary is the macro gear (rail, MP-E 65mm f/2.8), or flashes, or tripod (Giottos MT9360). Of note, even though it won’t carry the tripod, it will allow me to carry the monopod, by using one of the water bottle holders, and then wrapping the hand-strap through the hand-loop on top of the bag. I’m still watching for something which will hold everything the way I want, although much more weight will require a waist strap to better distribute the weight. Haven’t really decided what I want to do about this yet.
I also have a Black Rapid RS-7 strap. I really enjoy not having the camera around my neck, or hanging one shoulder. I was constantly having to pay attention to it to ensure it didn’t slide off. The Black Rapid sits diagonally across my torso, and keeps the camera within reach. It also has a couple of locking sliders which help keep the camera from moving around while you’re walking, but can allow easy access to pull the camera up for a shot.