Welcome, Fryguy!
You are going to have such a wonderful trip with your 3-year-old. We went with our 3-year-old and 1-year-old in July and despite the crowds, heat, and rain we had the best vacation of our lives. DS3 still talks about the trip EVERY single day!
I agree that you should go buy a guidebook or two, and then spend lots of time on these boards. The "WDW for Families" board below this one will be especially helpful if you have questions about strollers, rest times, etc.
Our 3-year-old was 42" at the time of our trip and went on (and loved!) nearly every ride that he was tall enough for. He tends to be hesitant so we were surprised that Splash Mountain and Star Tours were among his very favorite rides! He also especially enjoyed It's a Small World, Buzz, all transportation (monorails, boats, buses), Dumbo, Spaceship Earth (not my favorite, but he would have gone on it 10 times if we'd let him!), and many more. Meeting Mickey many times during the week was another special highlight. We skipped most of the parades and shows because our 1-year-old got too antsy, but I imagine your 3-year-old will really go for some of the great shows there.
Have fun!