How about labelling all those tunes that really get you going with the comment "Caffeine". The ones that are like an intravenous double espresso, that really grab your attention, make you jump around...whatever.
Create a smart playlist:
Comment contains Caffeine
This would make an ideal playlist for that ride to work on a morning.
On the other hand, how about when you don't want to be made to jump around, when you just want to relax and chill-out. Pick out all those songs that feel that a hot mug of cocoa and label them with the comment "Cocoa".