I use DisneyTime - it's great! Been running it since about Day 62 (and I'm now at 14 days 8 hours 17 minutes

) - it sits on your taskbar with a neat little Cinderella Castle icon. It stays hidden away, and you just brush your mouse over it to see how much time is left. It has other features, like trivia and a "notes" section, but I've found just the countdown enough reason to keep it on my PC. It has really helped in planning and with morale in planning the trip.
You can find it at :
DisneyTime
AEfx