Wizarding World of Harry Potter is great, make sure to get the park hopper so you an go to both sections via the train, which acts as a small ride as well (the ride is slightly different going each direction, so if the line is short and you have time I'd recommend riding a 2nd time going the other way). Butter Beer is awesome (try both regular and frozen). Make sure to stop in
Madam Fortescue's Ice Cream Parlor next to Gringott's bank. They've got amazing soft serve (if you enjoy the butter beer drink, the butter beer ice cream is top notch, but the other flavors are just as good). Like someone else said, Blue Man Group out in Universal Citywalk is awesome.
Disney World - like someone else said it's nothing like Disneyland. I would avoid Magic Kingdom unless you've got kids with you. Epcot, Animal Kingdom, and Hollywood Studios are much better options for adults. If you stay at one of the resorts you can also do a bar crawl on the Monorail going to the different resorts and getting drinks,
Epcot - Food & Wine Festival will be going on during your trip. It can get quite expensive if you're not careful but if you're not too concerned you'll have a blast. The SOARIN' ride is great, test track is cool, Mission to Mars is still good (and they just updated the video after like 20 years, lol). If your group enjoys those Short Films Pixar does, there's a "Short Films Festival" every 20 minutes or so over near Soarin'. It's a great way to spend a few minutes outside the heat, my wife and I do it every time we go (we have annual passes so that's quite a bit). There's also a soda shoppe near Spaceship Earth where you can taste free samples of soda from around the world (tip: DO NOT drink Italy's, but tell your friends to so you can laugh).
Animal Kingdom - The new Avatar section is amazing. The Banshee ride is one of the best rides I've ever been on, maybe even THE best. Wait times are insane so I've only ridden it once during a sneak peak for annual pass holders. They've also got some cool food and drinks over there. Mt Everest ride is very good, and if you can do the Safari at sun down you'll have a great shot at seeing the Lions roaming around (Safari is great either way).
Hollywood Studios - Outside of a few rides this place is still under heavy construction with the new Star Wars land. They do have like an Imperial March every like 30 minutes so if you're into Star Wars it's worth a few hours. You can knock this park out in the morning if you have the park hopper, but i'd rank it the bottom for now.
Other Attractions:
Volcano Bay - haven't been yet but heard it's fun for those who like water parks.
I-Drive - Home to the Orlando Eye (unless it's a super clear day i'd personally not recommend it), Madam Toussands, Ripley's Believe it Or Not, and I think there's a small Aquarium. A lot of good restaurants (and a lot of bad ones). Yelp is your friend. If you find yourself in this area on a Friday night the band at Tin Roof (right next to the Eye) is fantastic. Really good time. Be warned though, I-Drive is tourist central and it can be packed, so if you're looking for less crowds after the parks avoid at all costs.
Downtown Orlando - Honestly not much of a reason to go down here unless you're looking to bar crawl.
If you're looking for good food, Restaurants Row (Dr Phillips area) has some great stuff. If you have a car the Winter Park area has some great restaurants as well, but that's about 10-15 minutes north of Downtown, so 40 minutes from the Parks if you're staying there.
If you're wanting to drive out to the Beach, depending where you're staying Cocoa is probably the closest, but New Symrna is nicer in my opinion. If you're ok driving a bit farther and making a day of it the west coast has better beaches (Clearwater & Siesta Key), but they're twice as far of a drive.
