does anyone know anything about visa extensions?

i came into thailand with a 90-day non-immigrant type B visa so i could work for 3 months at a school. it expires just after my job ends. then i'll be traveling around the country, but by that time the visa has expired.

so far, all i got out of the school administration is that i can leave the country and re-enter, and that will get me a new visa. but that is not in my travel plans. is there a site somewhere with more information about visa extensions? has anyone done something like this?

thanks,
liz