I've had good luck with Standout Jobs, the 37signals job board, the joel on software job board and surprisingly even craigslist!<p>Also, there's startup jobs here from time to time (<a href="http://news.ycombinator.com/jobs" rel="nofollow">http://news.ycombinator.com/jobs</a>)<p>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.<p>Best of luck!
The best way to get a startup job is to network into it. If you're in SF, this is very easy - just go to all the web2.0 parties/meetups and you'll meet people hiring in no time.
I keep a fairly comprehensive list of startup job source here:
<a href="http://possibility.com/wiki/index.php?title=JobSearchSites" rel="nofollow">http://possibility.com/wiki/index.php?title=JobSearchSites</a>