It obviously depends on your game world. Create Water and Plant Growth never came up in my three-year campaign. It wasn't that type of setting.
I'd say "Detect Good/Evil/Law/Chaos", as well as any spell that acts differently for people of different alignments. (Cloak of Chaos, Dictum, etc.) At least in my game, those were huge -- both game-setting-wise, because there were big churches and governments using those spells liberally, and PC-wise, because at high levels, alignment-specific magic let PCs throw some heavy-duty area-effect stuff out there without damaging PCs who were in close with the bad guys.