This was tough, they are all good choices.

I do believe though that Captain Sim is top of the dogs on the porch when it comes to classical aircraft.

Although Airbus aircraft are neat, their cockpits are not all that difficult to render with all the CRT screens. This is not a bash against Airbus, I just think most aircraft with glass cockpits are produced by many third parties because they are considerably easier and faster to create. The old gauges on the other hand are a very different story, and most third party producers stray away from them or dumb them down. The only exception to this would be the A310.

Since the cockpit is my office, it's were everything counts to me, so I say bring on the legacy jetliners. DC10, L1011, B737-200, 747-200, and DC7. I also think a DC 8 Super 60 series would also make a good addition. No need to mention the B707, as I know it's already in the works. I too think the BAe 146 is also a good suggestion. Also, since most of these aircraft are getting scarce, I think it's important to gather the data on them, before it becomes next to impossible in the upcoming years as these aircraft retire and critical details are lost. My personal addition would be a Convair 580 or 640.

Cheers,
Thad