Here are some additional free Nebula stories:
Terry Bramlett’s novelette “Child, Maiden, Woman, Crone” from Baen’s Universe (thanks to SF Signal).
"The Evolution of Trickster Stories Among the Dogs Of North Park After the Change", by Kij Johnson, from The Coyote Road.
"Awakening", by Judith Berman - from The Black Gate.
The full list has been updated with the above three stories and can be found here.
The Nebula stories not available online are as follows:
"The Fiddler of Bayou Teche" - Delia Sherman (The Coyote Road)
"The Children's Crusade" - Robin Wayne Bailey (Heroes in Training)
"Unique Chicken Goes In Reverse" - Andy Duncan (Eclipse 1)
"The Story of Love" - Vera Nazarian (Salt of the Air)
Hopefully the authors or publishers will release those stories as well.