Here are some great lines I remember from strategy games: (not necessarily battle cries, but still.)
Lords of the realm II:
'We are British!' (crossbowman)
'We'll be shorn to pieces!' (peasant, while attacking)
Empire Earth:
'SIIIRE!!!' (probably some mediaeval unit).
'Saxon dogs!' (William the conquerer. while it is not so good, I remember I never figured out what he said until that one time, and because it sounds completely different than his voice acting in the campaign.)
'For honour and glory!' (probably knight.)
'For god and country!' (Probably pikeman)
'Attack, with sharpened steel!' (longsword, barbarian and probably others.)
'
Blood and iron!' (Guess who? This could actually be used as a battle cry.)
'Leave them alone, you shvine! (swine.)' (Manfred, in the campaign.)
Age of empires:
'Hayo! Hayo! Awonono! Awonono!' (of course, the priests. I even remember my friends invented a song about it.)
Age of Empires II:
'Heyaaaa?' and 'Yaaaaa?' (Gothic peasants)
Battle for the Middle Earth:
'It's time to get serious!' (Merry, or possibly Pippin.)
'We are warriors of the Shire!' (Pippin.)
'They appear very unfriendly.' (Pippin, while attacking.)
'Can I have some bacon?' (Pippin.)
'Ssssshhhhht, keep it down, keep it down!' (Ithilien Ranger.)
'21, 22, 23' (Legolas, counting kills, of course. However, he says it too quickly even for himself.)
'We ride, for the glory of Gondor!' (Knight)