I have bag type on my touring rigs and these euro-style panniers for commuting...think I got them from Nashbar 5 yrs ago...hey, they still sell them: http://www.nashbar.com/bikes/Product...0052_166983_-1___

They've been excellent for all commuting, and I routinely carry laptops and external drives back and forth. They lay fairly flat when not loaded and they have a little padding built in, two zippered pockets on the outside for keys, personals, etc. Perfect and inexpensive.