An awesome PowerPoint that teaches students how to combine like terms. Includes examples where students must use the distribute property. Also includes definitions for: term, constant, like term, and coefficient.
I use the metaphor of "herding sheep" for collecting like terms. Like terms are animals that are the same species (and may, therefore, be herded together). Before they are herded, however, they must all be busted out of their cages (the parentheses) using the distributive property.