It has been mentioned on the blog of Moonphase that there will be a 3rd season of Black Lagoon! Apparently it will be about the Roberta Arc, maybe about her past or something.
No date has been announced yet though.
I hope we get to see some kickass (Revy) action again ^^ I'm thrilled, will keep you posted on this one ;p
Source: Moonphase, Kurogane & DannyChoo