I'm waiting on two custom spec Hart barrels pre-fit for AR's, already have two others, no three, as Hart barrels were used by Remington's Custom Shop for the 40X when I bought it. Absolutely top drawer barrels and work, just prepare to wait - same with others.
http://www.hartbarrels.com/Pac-Nor Barreling is another, especially their Super Match stainless, with polygonal rifling, extremely accurate, easy to clean, and they make them with barrel nuts for Savage or Remington 700 drop-in installation. They also do the installation. Any contour, twist rate, number of lands and grooves, have it your way. I have many barrels from them all shoot .5" or better, some rifles have swap barrels in different calibers for varmint hunting. Never got a bad one yet.
http://pac-nor.com/Shilen, I rate these right up there, and they make them to your specs. Also make Savage pre-fits, actions, triggers and stuff.
http://www.shilen.com/Brux Barrels, cut rifling, good barrels, great accuracy, no problems.
http://bruxbarrels.com/ Krieger Barrels, cut rifling, great accuracy, no problems. They also have an inventory of popular calibers in stock.
https://www.kriegerbarrels.com/Gary Schneider Rifle Barrels, these are among the best, used by David Tubb, and mine proved very accurate. Makes polygonal rifling in certain calibers.
http://www.schneiderriflebarrels.com/Also, if you want to avoid the wait for a Shilen or Krieger check here, should the caliber, twist rate and contour you want be in stock, it will arrive in a few days, the last Krieger I ordered took just under a week.
http://www.brunoshooters.com/category/barrels.htmlFinally don't forget about Criterion Barrels. Formerly owned by Krieger, these buttoned rifled barrels are good quality. I ordered one in .25-06 Remington, a pre-fit for the Remington 783, in stainless, it arrived in slightly less than 8 weeks, cost was good, impressive quality and accuracy. Sold by:
http://northlandshooterssupply.com/ 
