During the BD-Live chat event with Terminator Salvation director McG, the director re-iterated his plans to make a Terminator 5 and Terminator 6 (via Gizmodo’s transcript of the event):
7:13: He just announced that he’s making another Terminator movie. Seriously.
7:16: …He said he’s making one after that.
7:46: He says Sarah Connor is going to be in the next film, but he’s not sure how he’s going to pull that off.