The Marlin xl7 suggested by prior posters is by all accounts an excellent value, but its not your only choice here. If you move up a hundred bucks or so, the field of available rifles really opens up.
Rifles available in the $400 - $500 (ish) range include:
-Savage 110 (I have one, and while its a good, solid, accurate rifle, I'm not as enamored with it as many folks seem to be;nothing at all wrong with this option)
-Browning A-Bolt Composite Stalker (I have never owned or shot one, but folks who have seem to like them)
-Remington 700 SPS (I've shot, but never owned these, they seem to be a solid value in this price range, although there have been internet murmurs of QC problems... who knows)
-Tikka T3 (I own 2 of these and love them both, really just an excellent value, can't reccomend them enough)
-Weatherby Vanguard / Howa 1500 (These rifles have a great reputation for accuracy and quality at an affordable price, I believe you can still pick these up at CDNN for sub $400)
-Weatherby Vanguard S2 (Not a whole lot out on these yet as they are a fairly new model, The info that is available looks pretty promising, and I'm trying to find an excuse to add one to the stable)
-Thompson Center Venture (An affordable new rifle with a solid reputation, haven't read as much about these)
-Ruger M77 (this one is a bit of a stretch pricewise, but various models are available at CDNN for just over $500)
The above is not an exhaustive list, but should give you an idea of some of the many options you may want to consider. As for caliber choice, I'm partial to '06, but realistically any of the ones mentioned thus far should do. Good luck with your choice.