I've been using this flight simulator since March:
http://www.gefs-online.com/
It's not bad for a free simulator and you can pretty much fly anywhere around the world. It could definitely be more realistic though (if you try it you'll know what I mean), but alas, it's free so I won't complain. Skydiving with the MD 11 (i.e., land a plane a quarter mile away from the airport at 30000 feet) is a fun activity .