I've listed:
Coves d'en Xoroi - for a couple of hours (avoid nearby Cales Cove without a 4x4)
Cala Galdana - for a day resort visit and Cala 'n Bosch in the evening.
Fornells & Cala Morell - both quite unique.
Monte Toro - the highest point on the Island.
The two main towns are worth a day trip both very diferent to each other, Cuitadela very Spanish and Mahon with a big English influence.
Lastly, we had a good day visiting a fort near Mahon, forgotten the name, there's lost of walking and its not everyone's cup-o-tea but I enjoyed it.
I've listed them here
linky.