Google Correlate  is based on technology they used to create Google Flu Trends. Google Flu Trends allows people to see where the flu pops up around the country by matching search data with location.

For instance, if a lot of people in New Jersey started searching for flu medicine, chances are people in that area had the bug.  This data could help medical facilities  send vaccines to the right areas if supplies were limited, and people in those areas could get ready for the worse when it looked like their area was getting sick.

Google released Google Correlate to allow anyone to find correlated data.

This also makes this a great keyword research tool for you!

While not perfect (a search for baby bibs said a related searches involve real estate) it may work for you. You can also zoom in on the results to see time frames when the most searches for those items occurred (fishing gear searches soar in the summer, for example).

Visit Google Correlate here to play with it yourself!