Discreets' Thermal Monitoring

so - i need to implement a component watchdog - as ::
if T aproaches critical - the pupply goes off (X) ASAP

what i need help for is (i need to monitor multiple components simultaneously) ::

1) any ways to set good thermal contact

2) the most simple ways to implement sensors (X) from common "stuff" (i'm happy to switch it of say 33% before specified thermal e.g. the accuracy is not so important as to know it "waves a flag" somwhere inside that 33%)

note: "common "stuff" " may be anything from electronic sensors to miniature mech. thermo-relays or other (i just donno anything about these things too well)