Depends a lot on what you fly and where. I'm strictly a GA man meself, and neither know nor care about tubes. But in the GA world, I'd recommend:
* RealAir Scout/Citabria/Decathalon, and Marchetti packages (the Citab is practically my default aircraft)
* Eaglesoft for Citations and technically complex singles & light twins
* Aerosoft Beaver and Twin Otter
I stay clear of anything by JustFlight or Abacus, because it's usually pretty second rate.
For freeware: Dean Baunton's Fletcher, and anything with the name Rick Piper attached (even his FS9 planes work in FSX SP2!). There's an FS9 Cessna 150 that works great in FSX, but I forget who it's by.
Regarding scenery, it depends very much where you fly. Creator has already listed the NZ stuff. For US/Canada/Europe there's Ultimate TerrainX from Flight1, does the same job as Christian's Topo. Photo sceneries abound. Airports are a bit thin on the ground, but are starting to trickle. This is a good place to start your search for freeware scenery:
http://walhalla.mine.nu/fsx.php