Corporate Sponsorship of a film, in any way, is a tricky thing. A viewer who becomes aware of multiple agendas in a film, generally is no longer going to be "with" the film. They become suspect. But sponsorship is not the same as turning your art into a commercial. There are many methods and many benefits to consider when considering corporate sponsorship (I will try to cover the negative side in another post in the future).
Perhaps the most important consideration regarding sponsorship is does the brand have a natural fit with your film (I know some will argue that the amount of money is the most important thing, but still). If the film and sponsorship is not aligned, it will read to the public as a crass money grab (which maybe it is) and they will approach the film from a feeling of distrust.
Brands have their own audience. Corporations maintain their own data on their "audience". This is what you want most from the alliance: audience sourcing. In considering sponsorship, ask them what they will do to reach out to their audience. This may very well be a much longer term relationship with many phases to it, but it's hard to leap into such an arrangement. As people like to say about investors and other supporters: "you have to get them pregnant first". It's surprising that such a caveman philosophy dominates in so many areas, but you get the logic. I prefer the "one step at a time" way of thinking myself.
You do need to keep the long term forever in mind though in working with a sponsor. You want them there with you ever step of the way, hopefully deepening their commitment with your combined success. Work the relationship. Give them new opportunities.
What do you want from the sponsorship from the get go though? Well, beyond building for the long haul, you want to do something that has immediate impact. Generally people think that is a big blow out party. Personally, I am not a fan of this approach, particularly at Sundance. They don't have much impact as they are over a few hours after they start. Further at many festivals, you are competing with many parties. And all parties get unruly; they just aren't a good experience and they don't leave much of a memory.
I am a big fan of dinners for fifty close friends. This approach only works if your publicist can get you high end journalists to attend. But who doesn't like a nice meal? The question is though how would this benefit the sponsor. Depending on your film and your sponsor,they may very much like the one on one interaction with your stars and team. They might want to offer this to their top level execs, as Sundance has become a bit of a corporate getaway, another perk in their arsenal. This approach can certainly extend beyond dinners: skiing with the stars, one on one sit downs, presentation of the movie at different branch offices.
Publicity materials are a relatively high cost item that you will need to have every step of the way. Will your sponsor pay for the cost of posters and postcards, t-shirts and hats? What can you offer them in return? Is it such a big deal to have their corporate logo on the poster? Is that too much to give away for such an investment?