I still need to learn how to kill shielders reliably, and I work on that by fighting very good people on the duel servers.
The way i see it, there are four methods of killing a shielder:
1) Use a very fast weapon and 'outspam' him. With that i mean: swing -> get blocked -> swing again (turn a bit into the swing to make it connect a bit earlier) and hope he also swings but is too slow.
2) Feint. Start a swing, cancel it (by pressing rightmouse) and quickly swing again. Hope the player isn't listening to block sounds or not paying attention. If a single feint fails, sometimes a double feint does the trick. However, keep in mind that feinting is very risky. You expose yourself to spam-style counterattacks.
3) Try to outmaneuver him and hit him from the side or back. This only works with high athletics, light or medium armor and even then it should be pretty easy for the shielder to keep facing you. Again, this relies on a mistake by your opponent.
4) Or, if the above tricks fail: Use a shield destroying weapon like an axe. Two handed swords also seem to destroy shields pretty damn fast.
Those throwing axes are also really bad for us shielders.
Als most of you know, 1) is my preferred method.
Another tip: In battle, i often ignore 'alert' shielders, switch targets and get back to that shielder when he's engaged with someone else. If all else fails, i keep smacking (spamming) that shield with my sword. Eventually, it will break.
(with the (heirloomed) steel shield being the exception)
I know i'm stating the obvious for you Braeden, but i felt like writing down some tips. I hope it helps someone.