Hi OleBear,
Simviation is the #1 resource for Flight Sim add-ons.
There are similar sites either independent or squad controlled but Simviation has been #1 all the time I've been 'flying'.
I don't think it would be very gracious of me to post any other sites on Simviation's pages but, if you would care to seek me out on M$'s games zone (CFS1/RidgeRunners) I will point you in the direction of some others. Sadly CFS1 & 2 are only being hosted on the Zone until the end of January so you will need to hurry if you want to find me (or anyone else for that matter, lolol).
Just ask for "Shades" and, if I'm not in this nic (by co-incidence I'm using the more festive nic; "Santa_Bare1" just at the moment), someone will point you in my direction. Failing that, any of my bud's will be able to help you with similar information. Just speak out on the main chat area and tell 'em I sent you (then run for cover, heheh).