My five:
Pierre de Fermat, if only for the real answer to his Last Theorem.
Caesar Augustus, to sort out Europe.
Evariste Gallois, a genius whose life was stupidly cut short.
Jesus and Mohammed, for reasons discussed earlier.
Cyrus the Great, to sort out the Middle East
John Candy… so he can make Uncle Buck 2 in 3D!
John Lennon and George Harrison… so they can do a Beatles reunion concert tour.
Lee Harvey Oswald…but only for a day or two… Interogate him in Gitmo… End of JFK assassination conspiracy theories!
My favorite grandpa who died while I was in the service. Just wanna say good bye.
Lee Harvey Oswald just to get a first person account.
Nick Drake so that he could see that he did make it on his own terms.
Hank Williams for the unwritten songs.
My son who didn’t make it through 48 hours.
And Adolf Hitler just so we could kill him again.
Heinlein, on the condition he write twelve more juveniles.
Was that a subtle dis against Yoko Ono? 
I’m not really all that excited to bring back historical figures. I’d bring back my mom, who died last year; my grandmother; and Steve Jobs, because I think he died way too soon and still had a lot more to contribute.
H. P. Lovecraft might be fun, because I’d love to see the expression on his face when he saw a plush stuffed Cthulhu.
Fredrich Nietzsche so that I could trim his mustache.
Virginia Woolf so that she could do some more writing.
Emiliano Zapata for Chicano pride.
Marilyn Monroe so that I could warn her about getting involved with politicians.
Jesus so that I could get a few things from the horses mouth.
Besides one’s that have been picked already; (Jesus, Abraham Lincoln…)
I would want to see Dr Martin Luther King Jr alive. I wonder what he would think about the United States in this age. I doubt it lives up to his ‘dream’ scenario… but hopefully there would be some pride in how much he meant to the, (then), future.
That’s funny cause Abe Lincoln and MLK were my 6th and 7th! I also thought of Hitler, if only to properly punish him. I don’t think there’s a death bad enough for him to suffer through, but it would be helpful, I think, for humanity to talk to one of history’s greatest monsters and understand him and see if there was any way to prevent what he did
I’ve always been curious about standards of beauty in the ancient world. I know about the weight thing, but people like the Four Beauties from ancient Chinese history seem like they would be very interesting to see compared to our modern standards. And to, you know, screw 
Stevie Ray Vaughn
Jeff Buckley
This was going to be my only answer. He’s my personal hero (even though I know he was uncomfortable with that concept) and I’m so incredibly disappointed that I’ll never get the chance to meet him in person (and I was nine when he died, so it’s not like I appreciated him before). We’d talk science and space and feminism and then we’d go smoke a joint.
I dunno about any of the Founding Fathers…they were pretty progressive folks, but I get the impression that they’d be irritatingly condescending to me, what with me having ladyparts and all. I suppose I could bring them here just to watch them get wasted and have screaming fights about philosophy.
Since we’re bringing back Carl Sagan, I’d also like to bring back Hypatia, just for the lulz. I’d love to see the two of them interact.
Carl Sagan. Other people on the board have said it more eloquently than I could. He’s been missed.
Alexander the Great. Died at 32 and did so much, but what could he have been if he’d lived longer?
Jane Austen. Because there aren’t enough women listed, and she is one of my favorite writers.
Jim Henson. Because I watched “Becoming Elmo” the other day and the scenes from his funeral made me tear up. I’ve been thinking about him a lot since seeing that movie.
Douglas Adams. Because I think he invented my sense of humor and I’d love to sit with him for a while.
I wish you’d asked for longer lists…there were a ton of people I’ve left off. (Next time would you give us at least ten? 
You can add more! To be honest, I had a hard time thinking up #5 until I realized Mohammad would be an interesting compliment to Jesus. I suppose I could have brought back all the FF, a ton of different religious figures, and others whom I may enjoy hanging out with, but feel free to put down more if you like
If we’re going for overall contribution then off the top of my head I’d say Nikola Tesla, Albert Einstein, Carl Sagan, Voltaire, and I’d need a couple of weeks to research and debate which major contributor to modern anarchist thought would be best to bring back.
There are some writers who never got to “finish” their lives and legacies, whether by dying while in the middle of writing something of import or by dying very young. I might look into bringing some of those back.
If I were to be a selfish experimenter, I’d maybe bring back Gengis Khan, Alexander the Great, any one historical personage the King Arthur legends are based on, Napoleon and perhaps Joan of Arc and let them all fight it out with their various motives and methods. I’d especially like to see Joan and Napoleon interact, and “Arthur” and Gengis Khan clash (if both have relatively well-matched armies). And if we’re bringing back more than five I might pick some famous warlords and leaders from cultures I know less about, just to add to the chaos.
I don’t see any point in bringing back Jesus to show Christians anything, because they’d just find some reason to believe it wasn’t the real Jesus. But I might bring him back out of my own curiosity on what his life was actually like. I’d like to know for sure whether he was literate, for example. Likewise I might bring Einstein back just to ask him what his damn last words were, or Alexander the Great to ask who he really handed his power over to on his deathbed.
I’d need more time to come up with the other three, but numbers one and two would be
Jim Henson
Walt Disney
I could see Jesus but I don’t believe he invented Christianity at all. That was Paul’s thing and they never knew one another personally. I would love to get them both together to hash things out in front of everyone.
Thomas Jefferson and Benjamin Franklin would also be useful to bring back as a pair.
My personal choice would be my daughter.
For some reason, the first person I thought of is the late, great Raoul Julia.
My maternal grandmother (she died before I was born)
My brother (dead at 27 due to a pulmonary embolism)
I’d have to think about the others.
I’d keep it personal and bring back my father and all four grandparents. My paternal grandfather I would be particularly interested in meeting. Born in 1876, he died just a few years before I was born, and he’s the only one I never met. His family were farmers in the Albany, New York area all the way back to the Dutch days, and they sent him to boarding school in NYC, where he eventually graduated from Columbia University in 1899. Then he moved out to Hollywood, California just one step ahead of the movie people. I’d like to hear his first-hand accounts of life back in those days.
EDIT: Whoops! Just clicked to the part in the OP about it having to be famous people. Oh well.
Douglas Adams
W.A Mozart
Albert Einstein
Carl Sagan
My friend’s sister who recently died because it is making her so sad.