Good luck with that. But since you asked, I use a arkel commuter pannier which I think is close to perfect. If it were rain proof with out using a cover, it would be the perfect.

In it I carrry pants, shirt, belt , laptop, keys, wallet everyday. I also have room to add and often do a pair of shoes, lunch, and still have room for the extra layer of clothes and gloves/hats etc. that I needed for the morning commute that I don't need for the evening commute. It's expandable, rugged, organized and the laptop sleeve is spot on secure. I challenge you to beat that.