Though almost all of these are in the here and now, and I offer no guarantees as to when they become very mainstream, here is my list of things, in no particular order, that make you go hmmm.
1) Net zero energy buildings
2) Radiant heating
3) Geothermal in places you thought it would not work
4) The new refrigerant that nobody knows about yet
5) Cooling beams in ceilings and walls
6) Building Information Modeling (BIM) 3-D drawings
7) Required air balancing
8) Biodiesel burning furnaces
9) Anything solar as it roars back from the bowels of the 1960s
10) Certifications for everything in HVAC.