If you are part of the JET Program, you are probably aware of the robust and cohesive communities JETs tend to form. In each region, older JETs train the newbies, helping them accustom to Japan by introducing local events and facilities.
Through generations of JETs, fantastic and comprehensive regional websites, wikis, and mailing lists come together. And usually, the managers of these websites and mailing lists welcome anyone in the local community to participate and make use of the information--not just JETs.
Some of the best events I've attended in Japan were ones I learned about by being involved in local JET mailing lists--even though I'm not a JET. As a student, I found seats on a dirt cheap tour package to Ise Jinguu and, later, I even found my first job in Japan thanks to mailing list posts that arrived in my inbox.
If you don't take advantage of this kind of resource already, I highly recommend looking into it. People regularly post free or cheap items in moving sales, cars for sale (usually a good deal, but not always), upcoming events, local Japanese language lessons, and all sorts of useful information. You can ask for advice about local gyms or even find buddies for a hiking trip or a weekend night on the town.
A partial list of groups and mailing lists sorted by region is available at jetwit.com, and another, slightly different list is available at the bottom of this Ajet.net page.
If you don't see a list for your region here, start by checking out the Facebook page. Post on the wall and ask if there is a regional mailing list. Most of the lists are run through Yahoo! Groups or Google Groups. Explain you are foreign and living in the area, and more likely than not you will be welcomed to the group.
For others of you in central Japan:
Gifujets Yahoo! Mailing List
naganojet Yahoo! Mailing List
Alternatively, you can search for a group in your area by typing in keywords on the main Yahoo! Groups page.