some of these have been mentioned before, but I'm going to list them anyway:
You're a Good Man, Charlie Brown
The Fantasticks
Godspell
The Last 5 Years
Putting it Together
The World Goes 'Round - FABULOUS!!!
I Do! I Do! is fantastic as well
Hedwig and the Angry Inch - if you can find someone with the talent.
I would have to disagree with LITTLE SHOP OF HORRORS. This show is by no means low budget - even if you skimp on the set, you can't successfully do the show without a convincing Audrey 2, which usually gets rented from MTI. And that alone costs a few thousand, nevermind the fairly high royalties.
Bronx, what do you mean by "small cast and low budget is off-broadway?" I don't know if you were joking or not, and I'm not attacking you or putting you down, but small cast and low budget isn't always off-Broadway. Most of the remarkable theatre I have ever seen was off-Broadway and most of the time, it's a whole lot better than ANYTHING that's on broadway. I'm not yelling at you or lecturing you or mean it in a nasty way, but don't always negatively stereotype off-Broadway as being "not as good" as Broadway, if that is indeed what you meant.
I'm not being nasty, I just want to know what you meant
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson