+1 on the Topeak DXP bag and rack system.

I have the Topeak Explorer rack and a DXP trunk bag with the quick release mechanism on my bike. I've had the bag for almost a year and have no issues with the zippers breaking, (which seemed to be a common complaint on the REI product reviews web site). Only issue was with the seams starting to give way where the panniers were stitched to the bag, but that was solved with a quick trip to the local tailors. The panniers are actually quite roomy and will hold a change of clothes, (including dress shoes), a lunch, a book or two, plus all the stuff you can fit in the trunk bag itself.

More than anything, I just like the freedom of having the bike carry the load instead of me. Its such a relief to get that damn backpack off your back, especially on a day like today when its 95 F out at 5:00 pm. I'm totally sold on the Topeak rack and bag combo - just surprised I don't seem more commuters sporting them. . . .