I have the 6 Million Dollar Crumpler and I absolutely adore it! I'm able to fit my Canon 30D, external flash and a couple of lenses in it and still have room for a wallet, iPhone, etc. It seems that there is always a nook or cranny somewhere in it that I can fit more into!
Check out
http://www.cambags.com/ ... they have photos submitted by real people showing what they are able to fit into each model ... something I found very useful when deciding which size to buy myself.