That was "No Children" by the Mountain Goats and it was a terrific choice. (And Paul and Lindsay's first dance was to "Nothing" by Jennifer Sawdon, who is married to Chris Geere.)
I loved the finale. Finding out that the flash forwards were not what they seemed was, frankly, a relief and it made me want to watch them all again, now that I know how it all turns out. Jimmy and Gretchen ending up unmarried (but still together) was the choice that made the most sense, I think. Paul and Lindsay remarrying...still not sure about that.
This was a uniquely great show and I'll really miss it.