The battery-powered Vent-Miser features a clock that opens and closes the vents at programmable intervals, completely independent of your thermostat's settings. So if your A/C doesn't need to keep your guest room cool on weekdays or if you only need to heat your bedroom at night, the Vent-Miser can automate this process for you, possibly saving you a few bucks in the process.

At about $25 a pop, the vents definitely lean towards investment rather than instant payoff, but they're a neat idea if you live in a house with crummy HVAC. [Amazon via OhGizmo!]