www.avsim.com is a great place to start. You have to sign up, but it is free....
The Airport Environment Upgrade is a good place to start:
[
library.avsim.net]
Meljet's awesome 777 (no virtual cockpit, but a neat plane nonetheless):
[
library.avsim.net]
Project Opensky's 757:
[
www.projectopensky.com]
Virtual cockpit textures for the above 757:
[
www.projectopensky.com]
Opensky's CRJ200:
[
www.projectopensky.com]
And also Opensky's Airbus A340:
[
www.projectopensky.com]
One of my absolute favourite addons is ActiveCamera, which gives head movement effects to the viewpoint. You can try the demo version around Seattle-Tacoma Intl (KSEA), get it from [
www.anticyclone.be] . If you're interested in this, let me know. It's really really good and used to be freeware.
Real-world AI traffic:
[
www.projectai.com] . These can be a bit difficult to get setup, but if you need a hand, I'm on MSN.
FSFrance's "Real Charles DeGaulle":
[
www.projets.fsfrance.com]
Also their Concorde, which is huge and difficult to fly:
[
www.fsfrance.com]
Unfortunately all the REALLY good files are payware, but if you have money to spend, I'd recommend PMDG's 737 (http://www.precisionmanuals.com) or their Beech 1900D.
That's about it, but if I remember post, I'll post them here.