Here's a few internal links:

Selma Song - Right! Right! (Len Chandler)
Walking with King (A song about freedom) - Marching with King by InOBU
Christmas in Washington (Steve Earle)
How Beautiful Upon the Mountain (Paxton)
Jackson C Frank's 'Don't Look Back'
EVE OF DESTRUCTION (from Barry McGuire) - Origins: eve of destruction

Several of those songs only have topical references to Selma itself but they're close enough to the theme I think they're worth relating.

Additionally, if someone has access to Sing Out! Volume 15, Issue 3 (Jul-65) it is reportedly titled "Protesters in Selma"

There's also WNEW's Story of Selma, which features the following songs:

Hold On (Keep Your Eyes on the Prize)        The Freedom Voices with Pete Seeger        2:55
We've Got a Rope That's a Berlin Wall        The Freedom Voices        2:10        
I Love Everybody        The Freedom Voices with Pete Seeger        3:32        
Pick 'Em Up and Lay 'Em Down        The Freedom Voices with Len Chandler        3:27
If You Want to Get Your Freedom        The Freedom Voices with Pete Seeger        1:05
Yankee Doodle (Wallace Said We Couldn't March)        The Freedom Voices with Len Chandler        0:41
Oh, Wallace        The Freedom Voices with Pete Seeger        2:52
Which Side Are You On? (Civil Rights Version)        The Freedom Voices with Len Chandler        4:21
Ain't Gonna Let Nobody Turn Me Round        The Freedom Voices with Pete Seeger        1:30
Ain't Gonna Let Nobody Turn Me 'Round (chorus)        The Freedom Voices        4:34
Do What the Spirits Say Do        The Freedom Voices with Len Chandler        2:26
Do What the Spirits Say Do (at Montgomery)        The Freedom Voices with Len Chandler        5:14
Freedom Now Chant        Len Chandler and Pete Seeger        1:33        
Murder on the Roads of Alabama        Len Chandler        4:02
(purchase album)