In a siege battle on hard mode (Sorry, I have no broadband for online play)I defended with a Germania force against a pre-marius Roman army. The hardcore of you out there, probably won't like this tactic, but it works.
I simply piled 4 units of German Warbands on top of each to create a dense phalanx. It meant all the Romans would be funneled onto the spears. At one point the formation started to swell a then burst, (this looks brill when viewed from above).
All the 'eager' romans pushing the 'broken' ones back into the spears and meeting their death
Also there is a great battle of me performing an ambush. I managed to Wipe out their general in less than 30 seconds.