I was discussing bicycle racks earlier. I really like the idea of managing your center of gravity, improving your balance, and moving the load lower on your bicycle helps. Here’s a bicycle rack that you can mount panniers lower down on.
Top bags for rear bike racks mount best with snap adapters. Here’s an Ortlieb snap adapter. However if you don’t need a top bag but just like the idea of clipping a raincoat or textbook to the top of your bike rack, you don’t need a bungee, you can use a rat trap.
For bike bags in general, Ortlieb seems pretty popular because they make a large selection of rubberized canvas bike panniers. So they’re good for all-weather travel, and you don’t need to monkey with separate pannier rain covers.
If you’re not concerned about rain, and want a clever way to rack your laptop, Ortlieb also has a laptop bag. I’d be a bit concerned about padding it, though. Taking a spill on a bike with a laptop on it could suck.