Fisherman is right on with his recomendations. Leupold VXIIIs are
GREAT scopes. Also look at Burris and Nikon. I personally love Bushnell 4200's ( partially because I get them at a very low cost ) but they are great glass for the money spent.
At the $500 range you are getting into great quality scopes for most purposes.
Take a look at
www.theopticzone.com
www.bearbasin.com