I have a SW-Mototech/BagsConnection Trial QL from Twisted Throttle
Clicky. The mounting system is something not previously mentioned in this thread - it mounts to a ring on the gas cap. There's pull cord at the front of the bag that releases a pin holding the bag to the mount, making it pretty easy to take off to fuel up.
The only problem that I have found, and I think it's easy to correct, is that with the handlebars fully over to the right, the starter button can get pressed by the corner of the bag. I'll be moving the adapter on the bottom of the bag forward to set the bag back when it's mounted on the tank.
I used to use a Rapid Transit bag that was just barely big enough for the two-way radio to fit. I still have it, but rarely use it now.
ian