Former Wonder Woman hopeful Adrianne Palicki is slated to join Agents of S.H.I.E.L.D. for season two. I don't know if she keeps trying out for this stuff or whether producers keep looking at her rocking body and dramatic face and think they have to get her in one of these comic adaptations. She appeared in the second G.I. Joe movie, so there's that.
Her character will be Mockingbird, real name Barbara Morse, a sort of Black Widow-esque character, which is to say that she doesn't have any special "powers" she's simply a kick-ass gal. The Mockingbird character has been around since the 70s but I'm not familiar with her. She apparently marries Hawkeye (played by Jeremy Renner in the Avengers movie) at some point and goes off to work on some team run by Agent Hill (Cobie Smulders in the Avengers movie).
I'm guessing this is part of MARVEL's attempt to add more universe characters to the series. No complaint on my part, I've liked Palicki since I first saw her in Legion.
Also joining the cast and upping the hotness quotient is Lucy Lawless, who will be playing S.H.I.E.L.D. agent Isabelle Hartley:
Must see tv indeed :-)