As far as side projects from the members of Phish this run and Trey playing with strings have produced the most most interesting versions of Phish songs.

Gordon started playing with The Duo (Marco Benevento on keys & Joe Russo on drums) after Phish's "breakup" in 2004.

This particular show features the premiere of their version of "You Enjoy Myself". If you want to hear an amazing version of YEM without guitar, here you go.

Of Phish note this show also features "Cars, Trucks, Buses", and a "Foam" as noted above that teases "Lengthwise", "Theme from the Bottom", "CTB", "YEM" and other holiday themed teases.

"The Trio", or "G.R.a.B." (Gordon, Russo, and Benevento), before they became "G.R.A.B." in 2006 (Gordon, Russo, Anastasio, Benevento), were a relatively short lived project.

Their shows are mostly "Duo" songs with a few covers and teases sprinkled in, such as Gordon singing Hanks Williams' "Lost Highway" here.

The complete list of Phish songs that this project covered, as far as I know, are:

Foam (with an hour long jammed out version from Atlanta)
Mike's Song
Cars, Trucks, Buses
Theme from the Bottom
Lengthwise
and
You Enjoy Myself

if you track down these recordings you can make a pretty awesome EP