They usually always have a festival or something happening downtown by the river. You can boat there and hook up at the public docks. The real action starts after 10:30 downtown. Lots of bars, pubs whatever and a lot of single girls (or least without their boy friends or husbands).
San Carlos Island (right before Estero by the beach before you cross the BIG bridge) Boat into the Bridge restaurant. Especially on Sunday afternoon they have Reggae music and losts of women! You may want to try the Channelmark restaurant. Right around the corner from the Bridge Rest. They have docks too.
The beach is ALWAYS great. Go to the Gulfshore Rest(the Cottage, now has a new downstairs bar right on the beach) and hangout around the Lani Kai next door and walk through Times Square etc. In the evening at the beach area go to the Beached Whale.
Bonita has LOTS to do as well. Higher end restaurants etc. Go to a club called AJAI in the Promenade. Dress well. Go late and stay late!