I have always enjoyed Robert Bruce's March To Bannockburn (better known as Scots Wa Hae).

'Scots, wha hae wi' Wallace bled,
Scots, wham Bruce has aften led,
Welcome tae your gory bed,
Or tae Victorie!
'Now's the day, and now's the hour:
See the front o' battle lour,
See approach proud Edward's power -
Chains and Slaverie!
'Wha will be a traitor knave?
Wha will fill a coward's grave?
Wha sae base as be a slave?
Let him turn and flee!
'Wha, for Scotland's king and law,
Freedom's sword will strongly draw,
Freeman stand, or Freeman fa',
Let him on wi' me!
'By Oppression's woes and pains!
By your sons in servile chains!
We will drain our dearest veins,
But they shall be free!
'Lay the proud usurpers low!
Tyrants fall in every foe!
Liberty's in every blow! -
Let us do or dee!'

Address to a Haggis and Auld Lang Syne (hey, it's sung at New Years at at the end of Burns suppers, how can you not like it) are also favourites. I really do need to find a good book on Burns and learn more. I enjoy his writings.