I'm still loving my 75$ MEC bicycle saddlebags, mounted in reverse from normal(wrong side) to keep the weight farther forward but not get too close to the exhaust.
EDIT: here's a link, they are normally 99$ but I waited till some came up that were returned.
MEC World Tour 56L Cycling Panniers - Mountain Equipment Co-op. Free Shipping Available
-mostly waterproof by themselves
designed very thoughtfully, every strap ha a keeper, even the drawstring has a bit of velcro to keep it from flapping.
-have a hard back, are designed to snap together for carrying by hand
-light as they are designed for bikes
-efficient to organize, the pockets are excellent for a motorbike, and the bottom pockets have a second zip to allow access to the bottom of the main compartment.
-sensible quick release that isn't easy to figure out, so they stay locked when someone tries to grab them, but with a few seconds I can trip the quick release strap, and going over bumps they stay tightly locked to the rack.
-lightweight to mount, my rack weighs under 1lb and cost about 2$.
Durable, I've already had a few low speed falls with them, spilled gasoline on them etc.
One went up in flames fairly recently when my muffler came loose, but despite the burning clothes and epoxy glue etc from my tool bag, the pack itself only sustained a small hole.
-Easily replaceable around the world the rack fits basically any bike pannier that mounts to a standard bike rack.
-have proper rain covers that work excellently.
Here's a picture of them mounted on my '79 CX500, I'm currently in the Yucatan, back on the road tomorrow, they've seen a lot of abuse and I honestly expected them to fail with all the weight and bumping over bad roads, they don't show any signs of problems, other than the now patched hole from my fire.
As you can see, they are almost a full foot forward of where the rear rack is, they basically sit an inch below a pillions leg, and parallel to the leg. IMO this is much better for balance than hanging way out on the back.
Vancouver to Argentina, 2010-?