Benjamin Marauder 25cal, MSRP is around $500, but you can find it for under $450. Go to Crosman's website for specs, here: Crosman | Airguns | Rifles | PCP | Marauder Rifle (.25)
There are alot of good guns out there, but you'll be hard pressed to beat the marauder without going over $1000. If money is no object, look at Edgun, FX, Falcon, and Daystate. I particularly like the Daystates, but I have a hard time spending that kind of money on an air rifle.
The Webley Raider is a decent gun as well.