I have been wondering about this as my ring is becoming slightly loose after losing 10 pounds. When I reach my goal, I know it will be too big. I found some links online that might be helpful. They are solutions that might work permanently or temporarily, but would not involve an actual re-sizing. Some of them should probably involve a jeweler for the best results.
http://www.gemsondisplay.com/shopexd.asp?id=523
http://apparel.drleonards.com/Appare...y=17199200.cfm
http://www.easycomforts.com/EasyComf...:referralID=NA
http://viewithere.com/ring_guard/rin...FctY2godIScmkA
http://www.ganoksin.com/borisat/nena...zing-beads.htm
I also saw several message boards that says Claire's stores carry plastic ring sizers to slip onto rings.