You have this:

- Lock On Modern Air Combat (LOMAC)
- Falcon 4: Allied Force
- IL2 Sturmovik
- Microsoft Combat Flight Simulator 3

Not sure if they have demos. The thing is, they all are good or in a case, EXCELLENT (Falcon 4, which is what I play) and that the money is really well invested. My personal take is the Falcon 4, but you have to be a hardcore flyer to love this game, as the campaigns and missions are complex.