Well, the Shop-Vac & Ridgid brands are all I've ever used. Can probably buy online. It all depends on how large a tank, how strong a motor you need and what you're going to use it for. Most are Wet/Dry type but I'm sure you can buy non-wet if you really want to.
There are other brands too from:
STANLEY, DE WALT, CRAFTSMAN, QUANTUM & more.
You can buy them in all stainless steel tank/housing(mostly for water/wet fluids) used in medical/clean room type facilities and with HEPA filtration.
For the homeowner, I prefer all plastic tank w/~5hp motor & ~15 or so gallon tank and for wet/dry. What ever you buy, buy it once as they'll just about last forever. And you really don't need to spend GOBS of money either.