You may also want to have a look at Ibiza Town (Evissa) rather than San An.
Ibiza Town is home to the night clubs El Divino and Pacha, the largest club in the world Privilege (home of Manumission) and across the road Amensia are just a short taxi / bus ride away.
Ibiza Town is more friendly and is home to the clued up clubbing crowd, with its all night markets, parades and cosmopolitan bars in the old town mixing in with a varity of resturants and traditional spanish bars and british pubs. It is a slightly more grown up crowd who are up for a party in the clubbing capital of the world.
San An is home to British pubs offering happy hours serving people often between the ages of 15 and 21 who are out to binge drink, its home to some of the islands worst violence and problems. There as mentioned are some good places in San An such as the sunset strip for clubbers and Cafe Mambo, Savana, Cafe Del Mar, Coastline Cafe and Bar M are all worth a visit. However it has to be said I lived over on Ibiza and have many friends on the island, most I know find San An, espically the West End and embarrassment to the rest of the island and a large part of the problem causing decline in tourism over the entire island.