Are there sites where you can partner with others on ideas?
vabmit: http://www.cofoundr.com/user/loginCofoundr was started a few years ago by a Google engineer.My personal experience is that I've met the people I've partnered with on start-ups/projects in three places:  1. Local Entrepreneurs' Club (MIT e-club)
  2. IRC/Mailing list/Other online community (like lj/fb)
  3. Through personal recommendations from mutual friends

If you're not already attending meetings of a local Entrepreneurs' Club, I strongly recommend it.  It's a great place to learn the model of how a start-up works - how do you make money, how do you build a brand, how do you improve your pitch, how does funding work, etc.  It's like a real time HN.  The MIT e-club lets people pitch their start-up ideas at weekly meetings where the rest of the club gives feedback.Then, I would suggest you think about what technology will drive your start-up and what community it will focus on serving. By hanging out in the relevant places on line associated with the technology and community you're targeting you'll quickly be able to identify local experts.  You can approach them to partner with you or to recommend someone who might want to.  Those experts will be in a good position to help you evaluate potential partners.If you are technical enough to build a demo and a good pitch for your start-up and plan to take angel funding, you can ask the investor to hook you up with someone.  Investors tend to be locally well connected and know technical people with start-up experience who have had past successes.