Towers and their stone:
Built by Gods
1st: Ada-Mantia/Adamantium Tower/Direnni Tower/Ur Tower and its Zero Stone.
2nd: Red Tower/Red Mountain/Dagoth Ur/Vvardenfell and the Heart of Lorkhan.
Built by Aldmeri
Crystal-like-Law/Crystal Tower
White-Gold/Imperial Palace and the Chim-el Adabal/Amulet of Kings
Orichalc
Green-Sap
Walk-Brass/Numidium and the Totem of Tiber Septim
Snow Throat/Throat of the World
and on and on....
Possibly the Ceporah Tower from the Isle of Artaeum?
There is a theory that the Khajiit themselves could be a tower, and moon sugar is their stone.
We should remember that the Tower is an important symbol in Elder Scrolls iconography. It has mythical importance and great metaphysical power. Vekh http://www.imperial-library.info/content/tower of it, and it is an important part of the http://www.imperial-library.info/content/concerning-psijic-order-and-psijic-endeavor