A fairly large flea market I attended a few times last year, once with my friend Chris who set up a booth (I sold an old receiver and a cd player that day...) and once this year, so far. It's not crazy big like other state's flea markets but it consumes the entire Medina Entertainment Center lot and an entire gravel overflow section above the Center.
There's a lot of antique-type stuff that seemed semi useless to me, but people were buying it, tons of local-related sports memorabilia, and even a guy pitching "professional grade" rug cleaner a la Billy Mays! I can walk around for a couple hours easily. It has always been well attended the times I've gone. The organiser rolls around a different points with meat raffle tickets for $1, and there's a soda/mini donut wagon parked. All of that being said, it's a low-key, lazy affair.
Tip for first time visitors: if you're coming in from Minneapolis direction, make the turn just before The Medina (at the lights), the parking is in a grassy field behind the flea market. You can't miss it.
Edit: I should add that it's held on Sundays and has been known to cancel for weather reasons. read more