Among other things, I would buy Lucasarts, and force George on pain of death to dramatically improve the quality of future Star Wars movies.
I think I’d also drive Bill Gates into bankruptcy. 
I would find out if it’s true that “everyone has a price.”
(a) Take 500 Billion of it and make it generate 25 Billion/yr return forever (5%; conservative)
(b) Private foreign aid program. Where the beneficiary countries’ government officials don’t touch a damn dime of it, it all goes to disease/hunger prevention and small-enterprise development.
(c) Buy an established University. Become enrolled in it forever. And make it have sensible policies about everything from curriculum to not naming campus buildings after donors to funding women’s badminton just as highly as men’s football.
(d) Buy out Hugh Hefner, magazine, mansion, silk smoking-jacket, girls and all Heck, have him franchise me as the new holder of the name/title “Hugh Hefner”.
(e) Trade payoff of national debt to some country in exchange tor letting me have a chunk of territory as the Absolute Monarchy of Deliria
(f) Biggest. Orgy. Ever.
A trillion dollars, eh?
TACOS FOR EVERYONE!!!
The Academy of Brewing and Western Hoplology, giving four-year and graduate degrees in brewing, brewing science, hops and barley agronomy, history and sociology of archaic weapons, metallurgy, likewise with full apprenticeship programs in swordsmithing and a complete staff able to take raw 18-year-olds and turn them into seasoned Maitres d’Armes or the appropriate equivalent for any and all forms of combat practiced by Western cultures from ca. 1400 to ca. 1850.
A Trillion Dollars? Well, I’m with Daniel Withrow; I’d form an organization to deal with famine, and also reproductive health care and education for women worldwide; we gotta get a grip on over-population.
I’d also form an organization, or help fund existing ones, to teach and research sustainable agriculture worldwide; teaching people to grow their own food in the best means for the area without destroying the land is a great dream for me.
I’d start a fund to aid aging blues musicians, and educate, encourage, and teach younger ones. That’s a debt owed, for all the music has given me.
I’d fund a National Museum of Photography, with grants and programs to encourage young folks in a medium that has given me much pleasure in life.
I’d be sure to hightail it to Washington, too, and dangle sweet carrots onna stick in order to cut through the same ol’ same ol’. Hope I wouldn’t be corrupted by that same ol’, too.
Any left? Well, paying off my thirty acres would be swell, with enough to make a teaching farm, to teach to aforementioned sustainable Ag techniques for the rest of my life. That’d make me happy.
Lest ya think I ain’t selfish, I prolly would hit the used bookstore right off and spend a coupla thou…
Whata nice thing to dream…
Buy Australia.
First, I’d personally pay the best writers, directors, and actors to make big-budget versions of the works of Robert Heinlein, with me having creative control of the output. (-:
Foundations, scholarships, bursaries, thinktanks, etc. I would set up permanent structures to encourage the things I believe in. Advancement of space, free-market economics, studies into creating the perfect beer, etc. Gotta think big with a trillion bucks. Leave a permanent stamp on humanity.
I’d like a really nice telescope. More specifically, an array of Hubble-class telescopes big enough have an effective aperture big enough to spot geographic features on planets around other stars.
I’d like to live in a high place. So I’ll spend 100 billion on a space elevator, with my personal apartment at the top of it.
And on second thought, just making my mark on humanity isn’t good enough. I want to be the last human remains in existence. So, with my last ten billion I’m going to build an interstellar probe for my burial, with my DNA encoded in a gold recording.
Big spender!!!
A cup of coffee would cost more!!
Lots of philanthropic things.
Oh, yeah.
Buy Microsoft. Fire everyone (with a generous severance, but only you were a poor employee).
Make all of the MS software open source. (I bet in a year we’d have a crashproof Windows that would install from one CD.)
Hmm…
How about a trillion lottery tickets?
I’d parlay that trillion into some REAL money!
Thanks to Feynn and his figures, I would make 1 million people millionaires! 
Start a religion and promulgate the hell out of it.
Ok, I’ve revamped my idea a bit. I would do my best to purchase a surplus luxury cruise ship. I would gut it, so that it would support a population of about 50 with plenty of elbow room, and a minimal support staff for said boat (to be paid well, with excellent room and board).
I would purchase at least one Naval Cruiser as a protective partner, and staff it with equally well paid folks.
Float out to international waters, and declare myself independant.
Then I would try to find an island to purchase wherein I could make a small town for all my friends to live in. Styling of the village would be a hybrid of Classical and Gothic.
Continue to fund private space program with goal of creating an almost independant space habitat.
Personally, have the first 4 cyl. import running a 5 sec 1/4 mile. heheheh
And a personal weapons collection of incredible variety and quantity.
When not traveling, I would be dedicating my life to learning… philosophy, literature and a healthy amount of Martial Arts… everything from Shaolin Gung Fu to a study of La Jue de la Hache.
I’d use six billion of it to pay off every single NZ student’s student loan. And then I’d throw money at the government until they conceeded that free education should, perhaps, be free. (Got my loan balance today, feeling bitter)
I’d start up a newspaper. It’d be inteligent and well-written. Zoo babies wouldn’t make it past page five. The journalists would be well-paid. There would be no sensationalstic bullshit that the NZ Herald keeps publishing. It’d have a readership of about 300 people, and they’d love it.
I’d start up a bizzare reality series. Ten million dollars to the first person to rediscover Atlantis. Or steal my house. Or travel back in time and prove it.
None of my friends or family would ever have to worry about money ever again.
I’d set up scholarships for arts students, mature students, hell, everybody!
I’d support the arts in NZ. Especially theater - lots of acting scholarships, more local tv/films created.
I’d give money away to any charity I liked the look of, including propping up our strugling mental health services
I would have houses and houses full of books.
And when I’d finished making NZ a better place (ain’t nobody buyin’ my country Bippy!) I’d move on to the rest of the world…
I also forgot to mention, I would host the most wild party ever to be held at an SCA event.
“Yes, Anastacia, I need about 5000 10’ round pavilions. They can be set around the site where my motte and baily is being constructed. Talk to the stonemason for better detiails.”
And my fledgling war unit would have some of the best armor being made today, and no jobs to worry about or keep us from attending every good war in the Knowne World.
Also, a huge endowment to the SCA…
Since I wasn’t able to steal one like I’ve dreamed of since '69 I’d buy a supersonic jet and fly from Boston to NYC at MACH 1.1 at one foot above skyscraper level. That’s just to let everyone know who’s boss.
Then the real plan!
I’d buy a whole fleet of tankers, with destroyers and aircraft carriers with many more jets for support. Everyone of them would bear the logo of Drug Importers, Inc.
Then I’d turn that measly trillion dollars into some real money so Pinky and I can do things right!
Well I’d… I’d spend it all.
I would buy a very nice beachfront property in La Jolla and a BMW, and I’d finance the comfortable retirement of all friends and family, and put about fifty million dollars in the bank. I’d give the rest to charity.
The only problem is that if charitable organizations around the country (or even the world) had an additional trillion to spend in a short time, it would trigger hyperinflation. Consequently, I’d probably donate at a rate of about ten billion per year for one hundred years.
Which charities? Environmental conservations groups and lobbying firms, various organizations that bring food and medical care to the poor worldwide, medical research, scholarships for various different fields.
I’d buy the SDMB a faster server.