The transitions of ammonia, the most abundant top-heavy molecule, can be used as an easy-to-use thermometer of molecular gas. Over the last few years, a new generation of 1cm receivers at ATNF and other telescopes has been commissioned which enables astronomers to exploit this peculiar feature in far more objects than before. I will present results from extensive ammonia observations toward the Galactic Center, nearby starburst galaxies, and ULIRGS.