Microscope. I loved mine as a kid - my kids don't
Wobble deck - hasn't been played with ONCE! In over a year. Can't bring myself to throw it out, its as-new (obviously!) and it was expensive. Anyone want it?
Our dolls house is played with incessantly.
Lego - we have MASSES of it, but I can't say it is ever played with, sadly
Walkie talkies. We have barbie ones, bob the builder ones, motorola ones - never used. Bah.
Leappad, hardly used.
The most used things are anything arty/crafty, anything musical (small keyboard, recorder etc), children's chunky tape recorder and cd player, board games, sticklebricks, Nintendo DS, light sabres/swords etc, hobby horses and dolls prams and trollies with bricks, big tractors and trucks, brio train track (has to be best value toy ever), Tomy aquadraw.