I'll take a page from Jack7 and talk about general categories.
#1: COMBAT LIRBARIAN magic: Runes, sigils, marks, circles, oragami soldiers, secret pages....all of them made the "book-toting wizard" a flavorful choice for me.
#2: Interior Decorating magic: Animate objects, move earth, mage hand, telekinesis, even prestidigitation: when you want a room just right
#3: Divinations. Though D&D divinations were usually pretty dry, the spellcaster as a lore-seeker, who knew the mysteries of the universe and could find out which ancient spirit to ask, was always a fun thing to play.
#4: Summoning. Forget about the (often underwhelming) combat potential, I want to call up devils from the nine hells and ask them questions about the weather, and to summon succubi for a night of passion, or to just call up an invisible servant or a low-level angel to drag my rickshaw around town...
#5: Shapeshifting. Not the battle-druid bear-shifting, more the "I'm going to turn into a bird and fly this message into town," and the "I'm going to turn into a fox and observe you from under this bush"...they utility potential of becoming an unobtrusive animal, or even a fairly fierce one.
All of those were lots of fun for me.