I've had good luck with Standout Jobs, the 37signals job board, the joel on software job board and surprisingly even craigslist!

Also, there's startup jobs here from time to time (http://news.ycombinator.com/jobs)

Other than that, I'd also check the community mailing lists, the ruby-nyc list for example gets a lot of job postings! Another Rails specific place I've had interest from is workingwithrails - lots of people go through profiles there and send out emails.

Best of luck!