There is a great (free!) spaceflight similator called Orbiter (check out the review on The Space Review - 14 November 2005). I have played with it a few times and I love it. Actually, I wish I had more time to dedicate to practicing orbital maneuvers.
Well, there is now a new add-on based on Joss Whedon’s Firefly series! Thanks to the latest episode of The Signal podcast for the heads-up.