I've only tried two methods of carrying stuff to work, with my preferred being a backpack. Personally I don't want panniers unbalancing the bike and making it wider (even if it is only marginally), although I've never tried them, its how I perceive it. I can fit quite a bit in the backpack.....laptop and headphones, notepad, overshoes, 3 or 4 workshirts, my lunch and sometimes work shoes. It is quite heavy to lift but once on it's not too bad, plus it keeps me warm during the colder rides to and from work.
The other thing I sometime use is a large bum-bag, especially during the summer. Use the backpack on a Monday with all my shirts for the week (secured in a locker) and then leave the laptop at work if I don't need it with me.