I'm thinking about going with some custom dog tags. They'll be a lot cheaper. Plus with the laser engraving you can put text, graphics or both on both sides! Only thing is they are not trackable. But they'll be fun to leave in a cache or two.
http://www.dogtagsonline.com/engraved.html
http://www.dogtagcreations.com/
http://www.dogtagsinc.com/FullColor/plastic.htm
What do you guys think?