Dont forget that great british airliner, the trident! Although i guess the later models were 'four engined' they were tri-jets. Try david maltbys site for a great model with a great cockpit. I know its for fs2004 - mite work in fsx.....!
Il agree with the vistaliners 727, i havent found a better freeware 727.
Struggled with the L-1011 - its somthing ive searched for for a long time, although looking at the shots on here ive seen looks like the beta one is good. Though lack of a really great tristar either freeware or payware disturbs me somewhat - id certainly be interested in somthing which not only looked like the real thing but flew like it as well. (are you reading this PMDG and Level D?)
I think the aerosoft tristar looks good but it flies like a ford transit van. :-/ And as for the 'fly the tristar' package ive seen, well if it looked like a tristar that might be a good start for V2

DC-10 - not fussed, not really looked for one freeware. So i guess the ones mentioned here are pretty good!