If I bought a new pair of speakers today it'd probably be the MMGs - $600, everybody loves them, and a great return policy if you don't like 'em. Hardly anything to lose, really.
But if you're willing to go used, $600 will go so much farther... I saw a pair of Infinity (yeah, I'm a fanatic) RS 2.5 speakers go for just $400 on eBay, in perfect condition. You'd have to spend thousands today to even come close to those. If I was within a two-day round trip drive of those I would have gotten them.