+1 on the Wolfman Express. I did a fair amount of research before I bought mine and have had it for four months now. While I haven't ridden it in the rain yet, so far I like it for it's intended purpose.
I use it principally to carry my DSLR camera and extra lens so I can easily access them. It removes easily so I can take my gear with me and reattaches in just a couple seconds. The rain cover fits in the rear pocket and can be put on very quickly. All in all, I am very happy with it