I'll be at a conference at an on-site Universal Studios hotel this week. I've got pretty much all day Monday, and that will probably be it. (Unfortunately.)
What should be on my list? Harry Potter stuff is obviously a must. And I love coasters. LOVE coasters.
For coasters, definitely Hulk, Dragon Challenge (ride both sides - they don't share the same layout), and Mummy. Rip Ride Rocket at USF can be fun but it can also be very rough.
Definitely don't miss Spiderman and Forbidden Journey at IoA. Those are arguably the two best dark rides in the world. River Adventure, Ripsaw Falls, and Bilge Rat Barges at IoA are three excellent water rides if you don't mind getting wet. Simpsons and Despicable Me at USF are pretty fun simulators if you're into that kind of ride. Men in Black is a shooting gallery ride, similar to Buzz Lightyear at Disney but stacked with AAs and also a bit more intense. E.T. Adventure is a classic dark ride that uses a ride system similar to Peter Pan's.
Universal's attraction lineup is so good that it's almost easier to tell you what not to ride. If you're short on time, you can skip Disaster, Dr. Doom's Fearfall, and Storm Force Accelatron without missing much.
Are you staying onsite? If so, be sure to get your express pass at the hotel concierge. It's good for unlimited rides on everything except Forbidden Journey, which doesn't accept express. Use single rider for that one if you want to re-ride after seeing the stellar standby queue.
With an express pass, you should easily be able to hit everything you want at both parks, even in one day. If you can't get express, spam single rider lines on everything. You should still be able to knock out almost, if not everything.
One more thing - if you find yourself hungry in IoA, check out Mythos. It's one of the best theme park restaurants around.
edit - wow, beat a few times. Good to see this thread a bit more active.
Hulk is better than Mummy imo
They're both amazing but Mummy has such great presentation. Love the fire effects.