I bought a Kurakyn "Gran Tour" bag and it is great. It can sit on the back seat and has an adjustable lumbar support (acts as a back rest when on the back seat). Of course it also turns around and sits on the luggage rack if you are riding two-up or have something else on the seat. I think I paid around $130 for it - it comes with some attachment straps, a lock, and a rain cover. It has kind of an internal frame which holds its shape if it is empty. I haven't been sorry I purchased it. It is available at numerous web sites, just look for the best price if you are interested.
2004 Vulcan Classic 1500 - carbed
Grips, Freeway pegs, engine guard
Floorboards, Nomad rear seat,
Custom made luggage rack, Windshield & Lowers
Saddlebags, Passenger floorboards,