I had really good luck with an Eddie Bauer bag from Target (nice small, usable size for every day, on the go needs)--it lasted a while, but just as it was going downhill very fast I happened to find an identical one at a consignment shop!
Before my 2nd was born I bought myself a JuJuBe bag as a Christmas present. It was huge and handy. It's still in great shape; and even though I no longer need it I can't seem to get rid of it. But even better than the bag was the diaper pouch that I got at the same time--that I still use to carry spare undies/pants for my not 100% potty trained preschooler. Both bags are the same plain black color so DH has/had no problem carrying they around.