I don't think anyone in their right mind would call me a screenshot master

, but to my knowledge the freeware packages for FS9 which I have used and consider worth trying are:
Ground - bluesphere, lennarts, VOZ, silver wings, golden wings perhaps if you like ancient aviation and fancy setting it up...

Airports - Airport Environment 7, Real Environment pro also has some alternative textures, VOZ and Silver/Golden wings too...
Autogen buildings - Koorbygen/VOZ, other replacement packages for certain regions
water - real environment pro, ashars water, perfect water, morewater, inlandwater
sky - fsskyworld, real environment pro, perfect sky
There are more but I didn't keep them long...
As for planes, I usually just search at any site for the plane I want and 'photoreal repaint'. Screenshotart.com has some amazing repaints by Yago and Bananabob + others, though a lot are for payware planes, though not all.
If you are really serious about screenshots you need payware though, Ground Environment (or GEPro) and Active Sky 6.5, Flight Environment too is great.
Don't forget about mesh, and LANDCLASS files, they make a big difference

Hope this is helpful
Krigl