When I say power requirements, I mean that the headphone jack on your standard ipod/phone/integrated PC sound card doesn’t give enough energy to the headphones for them to work as well as they should. For these kinds of headphones you need amplifiers or some other similar good power source.
You can buy a refurbished pair of XB500s for $38 and free shipping on Amazon, and the XB700 for around $70 at the same place. You can rule out the XB700 since you don’t strike me as the kind of audiophile who has an amp strong enough to drive it.
If you like rap/hip-hop/rock, try out the XB500s. If they don’t satisfy you, or you listen to a wide spectrum of genres and need to hear every detail in a song, you can always send them back (if you buy via Amazon, which is really the best place to buy them) and get a pair of M50s. You can’t go wrong with either, but I’d suggest the XB500 first since it delivers stronger bass and is considerably cheaper.
P.S. Don’t buy anything from Best Buy unless you don’t like money, just sayin