They have been working on Starcraft Ghost for 5 years. It was supposed to come out for gamecube in 2003 but then it was changed to 2004, then to 2005, then to 2006. Now it's going to be 2007. Don't hold your breath though.
Another good old RTS is Total Annihilation. The sequel is coming out next year called Supreme Commander. It's going to be awesome.