I've seen nothing but good reviews on the
Genz Benz stuff, especially used, you can get a great deal on the G-flex series.
Mesa stuff holds it's value pretty well, so you won't see too many bargain prices on them.
One cab I was impressed with the amount of low end was the B-52 from Peavey. I'm not normally a fan, but they had some fatness to them.
Another option too, if you have the time and inclination, find a nice heavy cab and put your own drivers in. I did that with an old set of Fender Ohmaha's I rescued from an old bandmaster cab that was headed for the trash.
I dropped 'em in a birch cab I got on **** for $125, wired em up so the cab would run stereo/ mono and I have to say, this cab is pretty darn nice.
Or, like PCM said, buy some different drivers to stock your existsing cab with, and save some time. You'll be able to flip the original speakers I'm sure.
Let us know what you do.
Bamm