As another fellow camera nut the best thing I can recommend is this site:
http://cambags.com/

It has reviews of most major bag mnfd as well as pictures showing what each bag can hold. This is invaluable IMHO.

My current setup consists of 4 different bags. 3 Mountainsmith bags (1 backpack, 1 rectangle bag, and 1 top-loader (triangle shaped). I also have a Lowepro Nova2 AW.

Depending on how you plan on using the bag, consider water proof covers offered by Lowepro's AW serries as well as Kata bags (I would recommend the R-102 for a super nice backpack). Many Mountainsmiths also come with rain covers. When you are carrying 3-4k worth of gear in your bag it is nice to know that if you do get caught in rain, the only things that will get wet is you and not your gear.

Good luck. Searching for the perfect bag is near impossible because according to many, there is no such thing as 1 perfect bag that is right for all conditions.

Jeff