I have a 1988 Trek 660 that I believe is all original (except for the saddle- cool white Concor). The full specs are here: http://www.vintage-trek.com/images/trek/Trek88_1.pdf
~56 cm frame (Trek measured in inches back then)
531 Reynolds tubing
Biopace (oval) Ultegra chainring (very cool) 52/42
Shimano 7-speed 13-24 cassette
It is in pretty good condition, although it's not cosmetically perfect.
I bought it a few years ago (2007, I think) from the original owner when I needed a bike while my Six13 was being repaired. I like it a lot, but it doesn't have low enough gearing to do the hills and I am spooked to ride it since the knee injury because I haven't been fitted on it. It is mostly just taking up space and sometimes used on the trainer.
I am thinking of selling it because I am running out of room and this is the bike that I use the least and really doesn't serve a purpose in the stable except as a back-up road bike.
I haven't been following the used bike market, but I thought some of you might have some idea what this bike would be worth. I am thinking of asking $500 and trying to get around $400. Does that sound about right?