I used to own the Kata R-103 which was able to easily carry a large pro camcorder (Sony HDR-FX1), two spare batteries, shotgun microphone, 6 HDV tapes, wireless microphone set, and much more room to spare. Of course, it was all video equipment, but that gives you an idea on how much photography equipment can be carried. The bag's quality is incredible, almost feels bullet proof. I never worried about anything being damaged while being inside.
I currently own the smaller and less expensive Kata DR-467 for my DSLR stuff. It's a cool looking bag (more so than the R-103), has a smart design, and has a decent sized upper compartment to carry non-photo stuff. The quality is nice, but still falls short of the R-103. But, it's over a $100 cheaper.
I used a sony bag meant for the HDR-FX1, it works very well, lots of space, rain cover, only a 100 bucks. I have a GL2 plus all the video goodies so right now I have like 5 different bags