I considered a bunch of bags online, from the Domke to trendy options like Crumplers. I ruled out the Crumplers because I've not had success buying camera bags online (as far as making sure it's right, etc). I was in Indianapolis today so I was able to drop by a camera store and check some of the bags out, settling on the Domke. It's designed with a fully configurable layout: it comes with a kind of 'lens cube' that is a padded box lined with velcro, with more inserts inside. I took it all apart and set it up to hold my stuff, which it does admirably. In fact, without being a lot larger than the Pro-8 the bag manages hold a lot more stuff, largely thanks to its height (with plenty of room to spare it holds a 1Dm2n with attached 70-200 2.8, a 24-70 2.8L a 17-40L and a 580EX flash. Depending on how you configure it you could carry quite a bit more. The side pockets are padded and can also be used for smaller lenses).

On usage:

The bag is VERY well designed, and the customizable interior lets you set it up in a manner that works best for your shooting style. Now, it is important to note that this is from using it for journalism-- I was following a guy around at a slow jog for and hour and a half! I couldn't tell you if it's the best bag for nature (I'd guess that it's not) but it's dang well excellent for on the fly shooting. That you can put a flashgun in the side pocket means that if you suddenly need extra light, voila you can while out a 580 without even having to look. The other side pocket comfortably fits a 20D with grip; no worries about having a backup camera crammed into the bag. The back of the bag has an open pocket: this is a Godsend for things like loose papers like notes and passes, etc.