Polish Harvest Festival 2012
When I went a couple of years ago one day was a Slavic Cultures Festival, too, and there were Croat, Czech and Ukrainian booths in addition to Polish. I had some good home-made Ukrainian food and pastries but the website only mentions Polish food. I hope there's something other than Polonia to sample.
Modest entrance fee, free parking, not much of a traffic hassle; the only problem will be if it rains and the vacant lot where you park is muddy, I guess. It's right down the street from Polonia.
I think I'm going to try to go on Friday.
Speaking of Polonia, the store and restaurant, for any of you that are not familiar with them, they do a terrific job. We often stop by that store for sausages, cheeses, sweets and treats. Their sauerkraut is particularly wonderful - nothing like the canned stuff you buy at the supermarket.
In addition to the food, they usually have a small but nice selection of handicrafts; in particular, holiday items. I'll be going by there soon to see what they've got out for Christmas, and every Spring, I buy a few of their hand-painted wooden eggs for our Easter table centerpiece.