Add Univega, Centurion and Miyata to the list - all of them are good Japanese machines.

They can be hard to find in great shape, but there are lots in OK shape I think, and I still see them on craigslist occasionally. I found a Peugeot hanging in someone's garage and bought it on the spot this fall. And I fixed up a Centurion for a neighbor last year.

I may look for a Japanese one next. Many of them have good solid alloy wheels and cranksets. My old Peugeot had neither, btw. But my ultimate mixte is the one I foolishly sold years ago when the mt.bike craze was young - a Motebecane Grand Touring.

The other thing to consider is drop bars vs something more upright. I can't understand drop bars on a mixte, unless you're planning on touring with one.