Sarah Michelle Gellar. Obviously. I miss her on screen and I'm sad that she never really got another breakout role after Buffy ended. I really wish The Wonderful Maladys, her HBO pilot from 2009/2010, had been picked up, because that role would have been so perfect for her and the pilot script was so good. Much much much better than Ringer, The Crazy Ones and Cruel Intentions the failed TV sequel.
Other than that, Lauren Ambrose from Six Feet Under, also miss her on TV and would like to see her in a show again.