My favorite trick lately is boring, but effective:
"Something Between Us"
When an opponent's mage or creature is causing trouble, and you want it gone for a while, how do you get rid of it? For 8 mana I love to Force Push something, and then put up a Wall of Thorns or Wall of Earth. The thing is now effectively 3 squares away since it will have to go around the wall. Sometimes it's worth the extra 3 mana to put them through a Wall of Thorns. They can walk back through such a wall, but once again it will take their whole action and it won't do anything until the next turn.
I have found it can also work very well if the square in question isn't important to just walk away and throw up a wall between your mage and the square they were just in. This saves the Force Push and 3 mana.