Here's an interesting find (thanks to the folks over at WrittenRoad.com for the tip). Mastheads.org "is a totally free, totally open, collaborative resource created in May 2006 by a writer/editor in New York who wanted to organize her collection of magazine mastheads and decided to do it online. With the help of other freelance peeps like herself, 15 mastheads turned into 70, and now the goal is to get every major title out there, with up-to-the-minute updates and staff changes." Benefit from the findings to date, and add to the collection if you're so inclined.
UPDATE, July 20, 2006:
Well, that was fast. Seems that this resource is no longer free. That's too bad. (If you become a regular contributor, however, you can still access the full database free of charge.)