If you're making batter that you need to pour (pancakes, anyone?), you can save yourself a step by mixing it in a disposable bag. Cut the corner and pour the batter directly from the bag.
Photo by Yammie's Noshery
WonderHowTo explains this easy trick:
You simply put all of the ingredients in a ziplock plastic bag and mash them around until they're thoroughly mixed together. Then, snip a small corner (make sure it's small, since the batter will be runny) off the end of the bag and dispense it into the muffin cups.
The bonus feature of this tip is that the bag lets you pour the batter without the spillage and waste. I'm always getting batter everywhere and this acts like an impromptu pastry bag.
Mess-Free Muffins: No Mixing Bowl Required [WonderHowTo]