I can't pick one favorite so here's a list of a few (Mac and solo) that spring to mind:
Someone's Gotta Change Your Mind - Lindsey Buckingham (Gift of Screws)
Edge of Love - Billy Burnette (Are You With Me Baby)
Better Days - Bekka and Billy (Bekka and Billy)
Dust - Fleetwood Mac (Bare Trees)
The Shape I'm In - Fleetwood Mac (I'm not sure which album it's from originally, but I have it on a disc called The Fleetwood Mac Collection)
I Got It In For You - Fleetwood Mac (Time)
I'm So Afraid - Fleetwood Mac (The Dance)
Sunny Side of Heaven - Fleetwood Mac (Bare Trees)
Planets of the Universe (demo version only) - Stevie Nicks
The Chain - Fleetwood Mac (The Dance)
As Long As You Follow - Fleetwood Mac (Greatest Hits)
Help is On the Way - Billy Burnette (Between Friends)
Beautiful Child - Fleetwood Mac (Tusk)
Go Insane - Fleetwood Mac (The Dance)
The Smile I Live For - Christine McVie (Christine McVie)
Come - Fleetwood Mac (Say You Will)
Hypnotized - Fleetwood Mac (Mystery to Me)
That's All For Everyone - Fleetwood Mac (Tusk)
Surrender the Rain - Lindsey Buckingham (Out of the Cradle)
Heart to Call Home - Bekka and Billy (Bekka and Billy)
Without a Leg to Stand On - Buckingham Nicks (Buckingham Nicks)
In the Back of My Mind - Fleetwood Mac (Behind the Mask)
Battle of the Dragon - Stevie Nicks (I only have it on the Enchanted set)
Peacekeeper (Live) - Fleetwood Mac (Say You Will)
Through the Walls - Bekka and Billy (Bekka and Billy)
oh yeah, and absolutely anything any of them ever did with Walter Egan or Tom Petty.
I guess that was more than just a few.