We have been taking our son since he was 6 months old, he is now 5 and I can tell you that things that scare him now didn't at 15-18 months.
FEAR is learned by humans, so a small child may not be frightened of the Haunted Mansion or other "scary" attractions that a 3-6 year old may be scared to go on.
At the age of your child our son went on every attractio0n that he met the height requirement. Also, take some time to allow you child to explore the "NON-ATTRACTION" WDW. Feeding the ducks pop corn by the Castle in MK, playing in the fountain at Epcot, watch the face light up and explore the sights of lights of WDW.
But, remember you know your child better than anyone else. This means that becauseone child loved all rides, doesn't mean your 17 month old will. Some, little one go happy crazy over the characters, other toddlers run for the hills as fast as their little legs will carry them.
We raised our son in amusement parks from the time he was 3 weeks old and by good fortune we live near one seasonal park (HersheyPark), so he goes to the park alot. He can do and is more open to do more than most 5 year olds, but still has that tinge of fear in him. He goes on everything his height allow at least once to see if he likes it and then decides if he wants to do it again.
As the other post said the transportation was and still is one of my son's highlights of his WDW vacation - monorails, boats and bus travel is great for him.
I think that if you go and allow plenty of time to just roam around the parks you will find that your toddler and you will find lots of things to enjoy.
We as adults forget that young children can find enjoyment in an empty box at the holidays, where we look for what's inside. WDW is much the same, they will find magic in the little things that we as adults will walk right buy.
The trains at Germany is a NOT TO BE MISSED attract for my son, but many adults will not even give it a second look.
Go to a website that has the height restrictions and then start selecting rides and attraction you feel your child will like. Use that as a guide, but always be flexible with children.
Some suggstions my son always liked:
MK:
Wedway People Mover (now called TTA) - relaxing monorail ride around Tomorrowland
Buzz Light year - the lights, colors, sounds are very stimulating for a little one
Jungle Cruise - lots to see and fun for the adults as well
Pooh - great ride nothing too scary - once again great color stimulus
TRAIN - especially for a boy, what male at any age doesn't like trains
Epcot:
Spaceship earth
Land boat ride
Imagination (some air poofs may scare child as there are sudden)
Studios:
BEAR IN THE BIG BLUE HOUSE - music, characters from the Disney Channel, fun time for the child
AK:
Lion King
Tarzan - both shows have music and movement to entertain the child
Safari - bumpy ride, may put the child to sleep, if not you canpoint out animals to them
Rafiki Planet Watch - petting zoo and train ride to get there
All parades are good as well.
Hope you have a great time.