best material for sticking power electronic devices into the heat sink
It depends on the uses you want to do with the paste?
Given your constraints, there's an excellent article at http://www.tomshardware.com/reviews/thermal-paste-performance-benchmark,3616-5.html 

For the sake of having something easy to use, you can use a Thermal Adhesive Tape Pad, if you don't mind the compromise in thermal conductivity.