April 2nd, 2015, 16:22
Two names to look for: Raimondo Taburet, and Justin Tyme. Plus, anything that has FSGenesis and freeware in the same sentence. There's quite a bit to choose from out there, and nearly all of it excellent. There's also a set from SOH user "rhumbaflappy" that was "marketed" for the CFS2 crowd, but that Sim uses the same scenery engine as FS9.
Also, to make the most of any mesh, open your fs9.cfg and go to the section. Edit the TERRAIN_MAX_VERTEX_LEVEL line and raise it to 21.