New Microsoft Flight Simulator X is due to ship in FY06Q4. From the stats, this will be the best Flight Sim allowing a true real gaming experience. It will also serve as the true benchmark for games on the new OS, Vista.  

http://www.microsoft.com/games/pc/flightsimulatorx.aspx

There are also a number of flight sim design groups. IFSD - Irish Flight Sim Design creates special scenery for MS Flight Sim 2004. http://www.ifsd.ie/

Screenshot is of the IFSD add-on scenery for FS2004 detailing Dublin Airport, Ireland.

Trailer

Check out guys the new trailer for Flight Simulator X....as real as it gets compared to v6 (1998), 7 (2000), 8 (2002), 9 (2004)....http://www.youtube.com/watch?v=ApqyUhPKV3o

Demo

You can also download a trail version which includes two airports, three missions, and three different aircraft. All of the missions take place at St. Maarten in the Caribbean.

http://download.microsoft.com/download/4/7/7/477dcc35-0b98-42c5-b06f-7ded38a40491/fsxprereleasedemo.exe

System Requirements