Non-college hackathons are sponsored mostly from Platform Marketing departments that want developers to use their toolkits. Inspired by "the greats" like Twilio and 10gen, most developer tool companies are looking for ways to get their tools known and used by developers and are willing to pay to do it. Good examples are: Heroku, Pusher, Apigee, Mashery, Cloudmine, Mailchimp, Box, Firebase, Pearson, New Relic.
Some like Apigee will only sponsor if they can be the top prized API or headline sponsor for the event. Some like Mashery will try to convince you that they don't have money (they do), but that they'll bring a bunch of people to your event (they wont), others like Microsoft will pay if you can integrate an appealing Windows 8 vertical, and then there are those like New Relic who will sponsor if they believe you are doing good for the community and want to show support #nerdlife (this is an extremely rare breed though, so don't count on finding too many like this). There are lots of Platform marketing teams out there with a lot of different budgets and reasons to sponsor. If you can align your hackathon with their initiatives then you can land some good ones.
After that, there's recruiting -- The recruiting bucks come easy if you're a top tier engineering school. Most of the big companies I know only want to hire top devs and will pay for creative ways like this to brand themselves to them. The only non-college hacks a recruiting sponsor will pay for are the mega hackathon events that bring everyone out of the woodworks - (ex. Photo Hack Day, Disrupt Hackathon, AngelHack).
Lastly, there is sponsorships from organizations sponsoring entrepreneurship (Kauffman, BizSpark, Google Entrepreneurship, Ford). These deals normally take 6-18 months, but are completely worth it if you can land one. They cut monster checks (normally 6-7 figures) and will guarantee the growth and sustainability of your event. However, you have to prove you're creating a scalable model for entrepreneurship (ex. StartX, AngelList).
And should all else fail there are ticket sales. If you're scrappily putting your hackathon together, want to see it scale (which means hiring people to help organize), and you don't have big entrepreneurship sponsors onboard yet, then you should probably charge for tickets. Either that or be willing to pay out of your own pocket if ANYTHING goes wrong…. and like most events, it almost always does...
For us, hackathons are not about money. We prefer to partner and co-host hackathons with companies to who have similar values and credibility among developers that they've earned by participating and forming deep links into the developer community. These include but are not limited to Twilio, SendGrid, TokBox, Hacker League. We've all earned developer credibility over the years by helping developers on the ground, not by buying our way in.
We serve developers earnestly and will continue to do so at events and with partners that are aligned with our values.
Amit - Mashery
FWIW, my posts on sponsorship:
Getting Awesome Sponsors (for college hackathons): http://alexeymk.com/hosting-hackathons/index.html
Getting Your Money's Worth as a Sponsor: http://alexeymk.com/61608156/index.html