Mount Prospect's is on Sunday mornings (til 1, I think) at Elmhurst and Northwest Highway, through October. Park a block north at the library/civic center, and you'll probably end up picking up pastries from Central Continental Bakery.
Highlights include a knife sharpener, The Pickle Guy, and a place with multiflavored pasta.
I haven't tried the Piemontese beef or any of the bakeries, and I have probably bought random produce from each of the vendors.
There's someone who has wild mushrooms at outrageous prices ($40 and up per pound for chanterelles and porcini), I didn't feel that was a good value.
What is patriotism, but the love of good things we ate in our childhood?
-- Lin Yutang