There's the Museum on one side, and the bench on the other. But I've been in plenty of towns where the sides are reversed. I'm doing a poll so I can see which is the most popular side for the bench.
My bench is on the left side of Main Street. Personally I think right-benches are more common because while resetting I observed that I'd get right-side beaches more often than left-side beaches (beaches as in the shores where like, the dock is and stuff).
That's what I thought when I started playing ACNL. But then I went to other people's towns and saw that it changed. I only really did this poll to see which side Nintendo leans towards.
My museum is currently on the left, bench on the right.
I was sort of freaked out at first, because the first three times I played ACNL, I had the it the opposite way. I didn't know that it could be different.