Meaning:

• When spoken by a woman with a rising pitch, わ conveys the speaker's mild assertion or volition。It also shows the speaker's intimacy with the listener.
じゃあ、行くわ。Well, I'm on my way now.
 
• When spoken by a man with a falling pitch, わconveys the speaker's mild assertion。
これはいいわ。This is great.

Location:  Behind just about any part of speech other than a question or volitional forms.

Gender:  The falling tone is used by both men and women but the rising tone is used predominantly by women.

Level:  Informal

Alternatives:

• Women may use わよ or の instead.  Go to no (の)
もう行くわよ。I'm going.
明日行くの。I'm going tomorrow.
 
• Men may use ぜ instead.  Go to ze (ぜ)
泣いたってどうしようもならないぜ。Crying doesn't get you anywhere.

Warning: 

※わ may precede particles ね and よ。
        じゃあ、行くわね。Well, I'm going, all right?
        じゃあ、いくわよ。Well, I'm going.

※Do not confuse わ with は (not a sentence-final particle).