Here's a texting one that Andrew made me think of...
If you're in ABC keyboard and just need to go get one character from the 123 keyboard, like a ", Press and hold the 123 button and the screen will change to the 123 characters.
Slide your finger (without ever lifting it) to the " and let off of it. The screen will automatically snap back to the ABC keyboard. It saves a button push, you don't have to change keyboards every time you just need one character.
Cool trick if you text a lot like I do. It saves time.

Even if you don't end up using it, try it. It's cool. Intuitive and innovative, anyways.