Microsoft Flight Simulator, or FS98, is currently the most realistic civilian flight simulator available for the home PC.  You can fly a variety a aircraft, such as the Boeing 737-400, the Learjet 45, and even the Bell 206 Jet Ranger helicopter!  Some aircraft are more challenging to fly, such as the Extra 300S, while others are simple to learn and fly, such as the Schweizer Sailplane.  I would recommend getting FS98 instead of the other "look-alike" sims.  I bought my copy at CompUSA for $50, but there was a $30 mail-in rebate.