Magazines certainly used to want transparancies, but I was under the impression that most of them wanted computer files of a suitable resolution these days - after all, most magazines are type-set and arranged on a Mac, so why would they want to have the effort of scanning in?
Contact the picture editor, or the overall editor of the magazine (dependent on it's size) and ask him/her which format suits them best. You'll probably find that mags such as Homes & Gardens will be traditional and mags such as Rollerblade Weekly will be more flexible as it's the content, not the quality which is the focal issue.
Good luck, and let us know what you find out!
Rob