Coda Hale's bcrypt-ruby is the Rails' developer's best solution to the rainbow tables scare, but its API is a little counter-intuitive to me.
My current project has developers scattered throughout Minnesota, China, and various regions of Los Angeles. We're not all in the same place, we don't all speak the same languages, and even those of us in the same city could have trouble linking up on any given day (LA is a big place), so intuitive code is a major benefit.
Consequently, I added a couple convenience methods to BCrypt that I think will make it a little easier to use. Check the Pastie by clicking the link.