"sa" is not exclusively masculine, it's not 下品, and it's certainly "correct" Japanese.
It's pretty casual, so I wouldn't use it when talking to your boss or your Japanese teacher or whoever, but there's no reason to avoid it in the appropriate social situations (such as casual conversations with friends around your age).
One of its most common uses is in breaking up extended sentences, like:
こないださぁ、駅前歩いてたらさぁ、変なおじさんに話しかけられてさぁ・・・
Some people might look at this and say it's "bad Japanese", but fact is that many people (mostly young people) talk this way. That's why it's important (as KrazyKat mentions above) to pay attention not just to the language itself but who's saying it and what situation they're saying it in.
Personally, just watching Japanese television and observing people around me and the like, I can kind of get a sense for which people I want to model my speech after.
"sa" is also heard when calling someone to get their attention (actually, I was just called with 「ジョン君さ・・・」 about 5 minutes ago by one of my bosses).
Anyway, that's hardly comprehensive, but for what it's worth...