Note: If you want it to sound a little less minor, change the Am to a C at the end 
of the 1st, 4th and 5th lines, like I have in the last verse.

   Am              G Em  Am 
O come, O come, Em-man-u-el
     C             Dm G   Am
And ransom captive Is---rael
     Dm               C Em    G
That mourns in lonely ex--ile here
   Am             Dm  G   Am
Un-til the Son of God a-ppear
   G         Am      Dm G    Am
Re-joice! Re-joice! Em-man-u-el
        C           Dm  Em   Am
Shall come to thee, O Is--ra-el.


   Am                G Em    Am 
O come, Thou Rod of Je-sse, free
       C               Dm G  Am
Thine own from Satan's ty--ranny
     Dm                  C  Em   G
From depths of Hell Thy peo-ple save
     Am               Dm    G   Am
And give them victory o'er the grave
   G         Am      Dm G   Am
Rejoice! Re-joice! Em-man-u-el
        C           Dm  Em   Am
Shall come to thee, O Israel.


   Am                     G  Em    Am 
O come, Thou Day-Spring, come and cheer
     C               Dm  G   Am
Our spirits by Thine ad-vent here
     Dm              C Em      G
Disperse the gloomy clouds of night
   Am                    Dm  G   Am
And death's dark shadows put to flight.
   G         Am      Dm G    Am
Re-joice! Re-joice! Em-man-u-el
        C           Dm  Em   Am
Shall come to thee, O Is--ra-el.


   Am               G  Em  Am 
O come, Thou Key of David, come,
     C             Dm  G   Am
And open wide our heavenly home;
     Dm                 C Em    G
Make safe the way that leads on high,
     Am              Dm G  Am
And close the path to mi--sery.
   G         Am      Dm G    Am
Re-joice! Re-joice! Em-man-u-el
        C           Dm  Em   Am
Shall come to thee, O Is--ra-el.


   Am      C           G  Em  C 
O come, O come, Thou Lord of might,
     C                Dm G     Am
Who to Thy tribes, on Sinai's height,
     Dm                 C  Em      G
In ancient times did'st gi-ve the Law,
   Am             Dm   G   C
In cloud, and majesty and awe.
   G         Am      Dm G    C
Re-joice! Re-joice! Em-man-u-el
        C           Dm  Em   Am
Shall come to thee, O Is--ra-el.


I usually mute the high E string on the G chords, except for in the 5th line of each verse. 
~Enjoy!