A recent obsession with the song Seven Bridges Road led to lots of time on YouTube and Wikipedia, and even an actual book. I figure after making a little effort, it's worth putting together some of the information for others.
So, Seven Bridges Road was written by Steve Young and recorded for his album Rock Salt and Nails (1969). Here's a YouTube of a version by Young from his second album, named after the song:
There are more recent live recordings online and he plays and sings the song in a similar style, as a singer-songwriter.
In 1973, Iain Matthews, of Fairport Convention (and other rock/folk/pop bands) recorded the song with the harmonies that have come to define Seven Bridges. It appears on his album Valley Hi.
Who arranged the harmonies? Well, if it wasn't Matthews, perhaps it was the producer of Valley Hi, the former Monkee Mike Nesmith!
According to the photographic history book The Eagles: An American Band (p. 166), Don Henley and company would sing Seven Bridges Road in their dressing room as a vocal warm up before shows on their Hotel California tour (that album was released in late 1976). The band later performed the song on stage and a version of it was recorded for Eagles Live. The liner notes to Eagles : The Very Best Of (2CD) state that they learned the song from Steve Young, but they clearly borrowed harmonic ideas from Matthews. Here they are from Seattle 1977:
The Eagles version has become the most iconic, although Dolly Parton's all-star bluegrass band does a pretty fine job by it, too. Here's Dolly:
More recently, Keith Urban (Mr. Nicole Kidman) has been bringing up opening acts to sing the song with him. In 2009, Sugarland add two voices to Urban (as well as a mandolin). I have to say, one thing I love about Sugarland is how happy they seem to be to be making music. It's not perfect, but they're having fun and projecting that; a charming stage presence.
In 2010, Urban was on tour with Grammy winners Lady Antebellum. The female vocalist, Hillary Scott, doesn't seem to know the song as well as the guys, but she wings it and finds her harmony lines.
Finally, a couple of non-professional acts. The first is an earnest attempt, but the recording makes clear the problem of pushing the bass part too hard. Let it resonate, but don't sing it out, man. (Also, something's a little off with the guitar. That's the time to just pause out of this one...)
The second, by the Hartley Brothers sounds great (and has a terrific toy poodle pontificating).
A great song by Young, terrific arrangement by Matthews and Nesmith, and kudos to the Eagles for bringing it to the attention of a whole lot of people.