I can't figure out how to send a complaint to ABC.

Here you go: http://abc.go.com/site/contactus.html

Might I recommend that instead of just asking ABC to put it back on next year, ask that they rerun it during the summer?

I think a big part of the reason the show failed is the competition it had on the other networks. There's a lot less competition in the summer, and networks tend to be in the mood to try anything, especially shows they already have and can run at very little expense.

Seinfeld and Last Comic Standing both started as summer shows, and I believe that gave them the boosts they otherwise would not have had. Big Day is also really most appropriate as a summer show. I believe the best chance Big Day would have to make a comeback would be with a rerun of the series in the summer, which would draw attention, higher ratings and a greater demand for the show.

Good luck, and try to get as many people as you can to write in and let ABC know how wonderful Big Day is. Thanks!