Here are some useful links
http://www.orbithangar.com/ (major mod repository)
http://www.avsim.com/ (also has several mods but not as up to date, also need to be registered to access it)
http://orbiter.dansteph.com/index.php (orbiter sound and other stuff)
http://www.ibiblio.org/mscorbit/ (meadville space center)
http://sourceforge.net/project/showf...group_id=55046 (poke around the orbiter section and you will find alot of the planet textures)
http://www.geocities.com/fastheinz39/Saturns_Moons.html (outer planets for orbiter)
http://www.orbiterwiki.org/wiki/Main_Page (orbiterwiki)
http://sourceforge.net/projects/nassp/ (project apollo/NASSP)
http://koti.mbnet.fi/jarmonik/Orbiter.html (Interplanetary MFD which i personaly prefer over TransX)
Have fun