There's a steal on an EVGA SuperNova 550W G2 80+ Gold Modular power supply at B&H Photo this Cyber Monday. It starts at $86, but a 53 percent off coupon quickly slashes that down to $39. Add a $10 mail in rebate and you have a $29 power supply.
We've lauded the SuperNova for its efficiency, lengthy warranty and near-silent operation.
550 watts should be plenty for most gaming rigs, and the fully modular design means you only use the cables you need. That results in a cleaner case with better cable management.