Hey Dan!

The first internship I had at a startup I found on craigslist.

If that doesn't cut it for you, you can always check out YouTern (http://www.youtern.com/) and InternMatch (http://www.internmatch.com/).

Lastly, and possibly the most effective would be just going to local start up events and networking and asking around. The startup community (at least here in Montreal) is really friendly and are always up for helping others.

Good luck!!