Appropriate Income Sharing Percentage

I've independently created a database that's caught on quite well - currently being used by 21 non-profits in Massachusetts. A larger software development firm has taken note of this and is interested in forming a strategic partnership. It would still be my database, they wouldn't get the copyright to it or anything like that. And I would still do all the actual work on it myself.

Here's what this other organization would provide:

• Let me use their billing department to handle all the invoicing for me
• They have a marketing person on staff that would write about me on the company webpage and submit articles to local publications
• I would work in their office at least two days a week. (They have a giant office with tons of empty rooms.)
• The owner of this company seems like a super great guy and, I'm sure, would be very helpful in guiding the future direction of my database - both programming-wise and business-wise

Taking into account the above things that this company would be providing to me, what would be a fair percentage for future revenue split? So, like, if one of my existing clients paid me $1,000 to build a special report for them... how much of that would be fair to go to this partnering organization and how much to me?