What rails plugins are good, stable and *really* enhance your code?

Question

Anyone have a list of rails plugins that are both stable and give you enough functionality to be worth the extra effort of supporting?

Edit:

I am mos

Answer 1

restful_authentication for sign in, sign out, sign up.

paperclip for file uploads.

rspec and shoulda for testing.

Could you be more specific in what you are looking for? There are so many great plugins for so many different tasks, it's hard to guess the right ones for you.