Read back issues to see what they've done, what could be expanded on, and what could be updated. Read the calendar of events if they have one. You may be able to find a local event that you could cover for them. The ideas you get from this process should already be slanted for the particular magazine. However, there are a number of other good resources for ideas.
Newspapers are a wonderful source of facts, ideas, and names of people to contact for stories.
Look at the Travel, Business, and other special sections. Don't forget the Classifieds. They can be a place to pickup offbeat stories. The Yellow Pages often hold stories just waiting to be told. Burke related a story of a local company that makes the large, novelty-shaped hot air balloons.