First, good business relationships are two-way. What do they hope to gain from you? If it's just a logo-swap, who cares.
But here's some things that can work out:
- Marketing dollars. Not the same as co-marketing. Usually people ignore ads from well-known companies, so it's not clear that co-marketing is useful by itself. Funding for your own ads (with them listed in the corner or "powered by" or whatever) is terrific.
- Access to dev teams. I haven't heard of a big company volunteering to do development for a small company and giving up the IP. If that did happen, you're dealing with a non-stellar remote team, which also doesn't sound terrific, but sure free is free. This sounds unlikely.
- Sponsorship to events. Yes! Going alone is good; also carving out a section of the big boy's booth can be very good. Gives you legitimacy and gives them something new to talk about at the show.
- Reselling. Their salesguys sell your stuff. This is how IBM operates and is often the precursor to being bought out completely. This opens new channels not accessible to you, which is good. It probably means a ton of new features, training, and time, so be comfortable that the reward is waiting for you.
- Introductions. People answer the phone when the big guys call. Who else do you need to talk to? Ask for introductions.
- Funding. Big companies fund little companies all the time. VC money is often not "smart" money, but company money often is because they're more attuned to the market and opportunities. And of course it makes it even more likely that they'll buy your company eventually because it will be at a "discount" (in the sense that their investment comes back to them).