Er...hi...I'm new here.

I wanted to contribute a personal endorsement for Chrome messenger bags. Their padded strap system is far more comfortable than any Timbuk2 or other messenger bag I have tried -- it's one big padded shaped strap that goes over one shoulder that meets a standard webbing strap with a retro seatbelt buckle. That description is a bit crap, so just go check out the photos on their site, I guess. The only downside is that they look so cool you kind of give off a hipster fakenger vibe if you aren't careful!

I have one of these:
http://www.chromebags.com/products/bags/show/13/

However, I find that carrying a large load puts too much weight on my back, especially when being carried on one shoulder. For heavier loads, or for days when I don't feel like being encumbered (or when I just want to look like a bike dork), I use one of my Ortleib panniers (clipped to my rear rack), which I also highly recommend. It's nice to have options!