Last summer PBS frontline had a really interesting documentary about the HeroRat project in Tanzania. You can watch a the 10 minute video at the PBS site here. Here they mention the rats are being used to detect Tuberculosis but I have a feeling I'd read elsewhere the rats were also being trained to detect cancer. You can go directly to the HeroRat project site here, it's a little cartoony for such a serious subject but I love the animations. Check out the 'HeroRat Beginnings' and the 'Making a Hero' - I'm pretty sure that dog at the end is not thinking about mine detection.
There is a collection of articles about the Arabidopsis mine detection program here.