become an expert in collectibles. Buy low, sell high.
Whenever I walk into a toy section at Wal-Mart, I know how much everything is worth. Even shit that just came out yesterday can easily be double.
You can even scour Target endcaps for items of value. I just purchased another Xbox360 racing wheel by MadKatz. It was $17.48 @ 75% off. At Best Buy, it retails for $79.99. I'm almost sure I can eBay it for $50.