I just came across this list on Phil Taylors blog- It gives a nice summary of some (not exhaustive) of the freeware FSX specific aircraft compiled with the FSX SDK.
Why is this important? Because objects in FSX that have been made with the FSX SDK will give better framerates, use DX10 capability (if included in the model) and features.
The list is below so have a look, check out any aircraft that catch your eye and then feel free to post some shots/thoughts about it in the 'Aircraft' sub forum.
http://blogs.msdn.com/ptaylor/archive/2008...ns-and-fsx.aspx

