I gotta plug REI's
novara commuter panniers. They have some durablity/wear issues that can be easily remedied. But they're an awesome, less expensive option than the Ortliebs. Got 'em on sale for $55 each, carry a laptop, lunch, change of clothes, tools, etc. Already tested the crash factor. I have the laptop in a protective sleeve I stole from another backpack. I went over the handlebars at about 12mph and the bike flipped over me landing square on the pannier with the laptop. It crushed some almonds I had in an outer pocket and broke the key clip, but the laptop was unscathed. They attach/detach in seconds and are locked on tight.