I worked in Santa Eulalia last year, after work we used to head down to Es Cana a few nights a week. Theres plenty of cheap n cheerful bars, then after them head to charlies, just next to the beach.
Charlies is open till 4am, they have entertainment on till about midnight then have a disco. It sounds cheesy and is. Most people in there after midnight are between 15 - 25, and its easy enough to find your self a holiday romance too!
San Antonio or Playa D'en Bossa are much busier,but it does get expensive if you go every night. We used to try and get a few people together in Es Cana then share a taxi to San Antonio. After that we'd walk around in a drunken state till about 7 30am and get the 1st bus back to Santa Eulalia.
If your stuck theres a handfull of english places to check out anyway, The Queen Vic, Charlies (in Santa Eulalia, no connection) Mirage, and Guarana.