I just finished Jim C. Hines latest novel, Codex Born (review coming soon!) and I can't get over the insanely awesome magical system he created. Codex Born is a sequel to Libriomancer and the characters in the novel have the ability to reach into books and pull objects out.
Let that sink in for a minute. You open a book like Alice in Wonderland, for example, and you can pull out a piece of "eat me" cake. You could get a time turner from Harry Potter or a ray gun from any pulp sci-fi novel. It is basically the best magic system there is.
Then again, Michael R. Underwood has a series of books that has a magical system called geekomancy. Watching or reading something gives you it's power for a certain amount of time. Watch some Buffy, learn to kick ass. Watch the Avengers and learn to... well, kick ass. You get the picture.
Outrageously awesome magical systems are a dime a dozen in science fiction and fantasy novels. Most of them are also genuinely awesome. You could talk to spirits like Eli Monpress in Rachel Aaron's fantasy series, or use the power of the earth as a druid in Kevin Hearne's Iron Druid chronicles.
So, fellow readers, if you could have the magical powers from one book, which would it be? Are you going to be Harry Potter, or perhaps a Libriomancer? Maybe classic D&D magic is more your speed?
For what it's worth, I would definitely be a Libriomancer. How about you?