OK, I'm at home on a Saturday afternoon passing time and, encouraged by this thread and the McRackin-inspired desire to visit them all, I did a bit of torre research.
Torre de ses Portes is the one down near Ses Salinas. Built in the 18th century.
Morbyd said:
On my (slightly warn but much loved) map it says Torre de Campanitx.
Campanitx is also known as Torre d'en Valls. As mentioned above, it's near Es Pou des Lleo and Cala de Boix, with a view out to the island of Tagomago. Built in the 2nd half of the 18th century.
Torre de sa Sal Rossa is also known as Torre de Carregador. It's the one visible from Playa d'en Bossa. Built in the 16th century, it appears to be the oldest of the 7 sisters.
Built in the 18th century, Torre de Portinatx overlooks the town of the same name.
5 torre comte (it has another name i can't remember)
Also built in the 18th century, Torre den Rovira is also known as Torre de Comte. It's at Punta de sa Torre, in between Playa Comte and Cala Bassa.
Torre des Savinar is the one with the great view of Es Vedra and Es Vedranell. South of Cala d'Hort and Cap Blanc. Also known as Torre d'es Pirata.
Morbyd said:
Torre d'es Molar. It's just west of Puerto de San Miguel
Torre des Molar is also known as Torre de Balansat. Built in the 18th century.
There are also partial remains of two towers on the north coast at Cap d' Albarca. They're known as Torres d'en Lluc
In addition, my map shows one more tower on the island Sa Conillera, off the west coast near Playa Comte and Punta de sa Torre.
Aside from the 7 coastal torres, there are also plenty of torres inland of various ages and uses. This interactive website has photos of many of them:
http://www.ibizapocapoc.es/Marcos/entra/Guiafacil/Torres.htm
Sources:
www.eivissaweb.com,
http://www.ibizapocapoc.es, my trusty map