This is an old song that sounds lovely on the Piano-Accordion. 
(beginners can simplify Bdim/G to G and Am7 to Am). 
I suggest reading the history behind this song, because it adds a new depth to 
the understanding of the beauty of this piece. AMouse197.

http://en.wikipedia.org/wiki/The_Bonnie_Banks_o%27_Loch_Lomond
http://www.youtube.com/watch?v=Qu_aBryealw - this is a video of this tab being played

  
    G           Bdim/G           C           D
By yon bonnie banks and by yon bonnie braes,
           G           Em           C   D
Where the sun shines bright on Loch Lo-mon'.
      C        G                Am7          C
where me and me true love were ever wont to gae
        G              C            D  G
On the bonnie, bonnie banks o' Loch Lo-mon'.

Chorus:
   G             Bdim/G             C             D
O ye'll tak' the high road and I'll tak the low road,
     G           Em      C     D
An' I'll be in Scotland afore ye;
    C          G              Am7   Am    C
But me and me true love will never meet again
        G              C            D  G
On the bonnie, bonnie banks o' Loch Lo-mon'.

       G            Bdim/G         C       D
'Twas there that we parted in yon shady glen,
        G           Em           C   D
On the steep, steep sides o' Ben Lo-mon',
          C          G          Am7   Am       C
Where in deep purple hue the Hieland hills we view,
         G           C          D    G
An' the moon comin' out in the gloa-min'.

(chorus)
     G           Bdim/G            C             D
The wee birdies sing and the wild flow'rs spring,
        G           Em           C   D
And in sunshine the waters lie slee-pin';
          C              G          Am7   Am    C
But the broken heart it ken nae second spring again,
         G           C               D    G
Tho' the waefu' may cease frae their gree-tin'