I am a fairly large fan of Flight Simulator. I have FS2004 and play it weekly. I have also had FS98 and modded it to the point where it contained almost 100 planes. But FS2004 is a great thing to mess around on if you have some free time or you are just bored.
I also have the full thrustmaster setup so I have all of the pedals and joysitck as well as the throttle adjuster, which makes it even funner to mess around with.