I think any of Animal Plastics, Reptile Basics and Boaphile are all good choises.
The one thing I REALLY recomend is to get a rack that has at least 2 more slots than you have snakes. I used to say I would only get 4 snakes MAX. Well I'm up to 5 BPs and 2 baby Boas in the way...
I LOVE my 32qt x4 tub RBI rack. But I do regret not buying a rack with more tub space. I also regret not getting the 41qt tub version instead.
I know Boaphile has a nice 41qt 4x tub rack. RBI makes a much cheaper (as in price) 3x tub version. I dont know much about Animal Plastics.
EDIT: I forgot to mention the racks from RBI and Boaphile can be stack on top of each other (of the same type) for expansion.