I enjoy spellcasters and spellcaster-themed things. ~nodnod~
I never was able to put together a Spellbook deck due to financial limitations and certain cards being super-spensive, but I did have a very classic deck based on Magician's Valkyria, Secret Village of the Spellcasters, and Sorcerer of Dark Magick.
Then I had my Gravekeeper deck, which made the opponent mill a card for every time they declared an attack, and dealt damage for every card sent to the graveyard to be permanently locked away in the Necrovalley.
And my Endymion deck, with spell counters galore. Breakers, Defenders, and Royal Magickal Libraries abound. Tempest Magician would detonate all the spell counters for direct damage.
I think my favourite card would have to have been Magickal Dimension, though. It was so versatile! It could be used for monster destruction, as a summoning aid, used during the battle phase to declare one more attack than your opponent thought you could, or even chained on an opponent's monster destruction effect to cause it to have an irrelevant target! And because you don't have to choose whether or not to destroy a monster until it resolves, it didn't actually "target" a monster -- not even the one you sacrificed to cast it.
EDIT: Also, given the tags on the thread are already decidedly Abridged, may I suggest also adding "Motorcycles" as a tag? And card games thereupon. ~nodnod~