My son LOVED the Leapfrog Word Whammer - not the little fridge version but the bigger one. It plays music and is very engaging and the letters are easy for toddler hands to grasp. My kids are 19 months apart and his intense, persistent older sister kept me very busy, so I needed toys that would keep him amused. He got the word whammer at one yr (can't remember how many months old he was) and loved it. By the time he turned 2, he had learned all the letters. It was such a cool toy because a) he loved it, and b) he learned the alphabet from it (score! lol).
My son sounds like yours... fascinated by how things work. I was reading his baby book the other day and one of the entries said: "he loved to take things apart to see how they work!"
He went through a phase where he was constantly breaking things... sigh. He's much more careful now (he's 8) Phew, lol
Cricket - my son LOVES Play Doh too
What about Duplo blocks, or puzzles? (Ohhh... my son loved puzzles as a toddler! Memories...) He also adored Thomas the tank engine and would spend hours on the floor building tracks and bridges, etc. He liked to connect the tracks together so they'd go all the way down the hall - he thought that was pretty funny.