It's great when you have friends that have the skills necessary to do a project with you. But what if all the ones with skills are too busy, and the ones that have free time and want to work with you don't have the skills?
Where would you start looking for partners?
In the coffee shops near a university with a computer science department.
Mostly through networking. I would ask my closest friends for their recommendations, and then go outwards along my network from there (linkedin, facebook, etc) to find people who know people that I know.
Talk with the ones you feel are confident with but are too busy. Ask them to recommend folks they would want to work with. Typically, those with high skill sets tend to be pretty good at recognizing others with similar skills.
If you don't have a solid enough business plan or wouldn't have enough to offer the folks with skills, though, don't expect many qualified people to offer up themselves or peers too eagerly.
If you already know what you want to do for your project, you may as well get started on it on your own. If you have some tangible (though unfinished project), maybe some of the busy friends might be more interested, and even if not, you'll have something that will be more likely to draw interest from other potential collaborators.
If you don't have an idea already, I don't know if there's any great way to force it along without finding someone else who is already interested in doing something with you.
Try Craigslist, LinkedIn, and online forums. Hang around on the forums and see who looks like they know what they're talking about and then approach them. If they can't or won't partner, ask them for a recommendation of someone else.
I have to agree with Adam on the networking ideas. Really though, the bulletin board at the closest university's computer science building is your best bet. I picked up a project when I was an undergrad there myself. LinkedIn is a great resource, as are technology specific bulletin boards and community groups (i.e. Flex, AIR, PHP).
If you get really stuck, you can always try Craigslist but beware, you never know what you're going to get on there.
Easy, StackOverflow.com
Seriously though, if you starting looking for individuals you don't know personally, it's very easy to get burned. It's dangerous even if you are working with people whom you do know personally. Since it's for-profit, you're basically running a business. Running your own business is a difficult (if potentially rewarding) path even if you are your own boss, and not part of an equal partnership.
You probably want to look in places where a community has been established so you can have some kind of impression of what this person is like, their skills, their personality, etc. But proceed with caution.
Go to meetups in your area having to do with software development. If you're looking for a strictly-business type partner then go to non-development meetups. Check meetup.com in your area. Networking is king. Get out and meet people or die, is what someone once told me.
Also consider non-tech skills required to make a new venture successful.
As a consultant, I wouldn't be able to focus on tech tasks if I didn't have a capable business team to handle accounts recievable and payable, payroll, advertising, sales and client relationships.