I'm looking for a shoulder bag for 1 DSLR, 2 extra lenses and a small flash. I will probably be picking up a 70-200mm f/2.8 lens, so the bag needs to fit that attached to a camera. The bag needs to allow the camera to be easily stored and retrieved one handed.
Lowpro slingshot is an awesome bag. Has a built in weather cover for light rain, and enough extra storage for keys, wallet, neutral gray card, etc.
I've got a Tamrac Velocity 8 and love it. It's got good space, is very comfortable, and can be pushed out of the way easily.
Plus the accessory system makes it easy to add things like water bottle holders, filter pouch, etc.
Also, I was looking at a Tamrac Aero Speed Pack 85 yesterday and was quite impressed by it.
I'm leaning towards the Think Tank Retrospective 20 which looks like it meets all my requirements.
It's hard finding a perfect bag so here are my top picks...
Skytop Trading Leather Holster - This is my favorite case. I use it for general photos such as street, short hikes, and museums. (And I think it looks great.)
Lowepro Faskpack 250 - I use this for travel. Holds several lenses and bodies and I have even used the laptop section stuffed with a camelbak water bladder before camera bags with bladders were popular. You can even swing it off one shoulder and use it like a sling bag.
Tamrac Velocity x10 - My gear lives most of its life in this bag... mainly for it's size. It's a HUGE sling bag but it's not very comfortable. After 6+ hours of carrying this packed with pretty much all of my gear I realized that this monster is best at just getting me from point
B. I do like the fact it is so big I can keep my cameras with lenses and hoods mounted and the lens caps off. This allows me to switch camera quick, but at the expense of bulk (and weight.)
I use pentax crossover one. Lightweith and I can put Camera with one lens mounted + 2 others lenses (or even 3 if lens are small - like fixed focal ones) as well as extra stuff like battery, memory card, ... in the upper part
I use a Lowepro Minitracker backpack but there are so many alternatives.
This is a nice site with pictures of many bags incl equipment: http://www.cambags.com/