Hard to beat a Leupold Mk4 for price/durability/performance. Leupold offers alot options as well. Im partial to them because in our sniper section we have an m14 that needed an optic and an email to leupold was all it took and they sent me a mk4 3.5-10 scope, 12-40x60 spotting scope, a set of rings, and even threw in some hats...for free! They have great customer service and as they have proven to me, they support our troops. We also use Leupolds on our M107's, M24's, and M110. They are a quality scope for sure. Other scopes id recommend are US Optics, Nightforce, IOR Valdata, and Schmidt and Bender. It all just depends on your intended use and how much you wanna spend.
I second pretty much everything that B4Infantryman said, Leupold makes a good product that is 90% of what you get in a Schmidt & Bender or Nightforce. If the extra 10% is worthwhile to you, or if you are taking extremely long range shots (800+) I would opt for the better glass with any of the names above.
US Optics, Nightforce, Schmidt & Bender, etc. are all world class scopes, and you can notice a difference.
I don't consider my 16" SOCCOM M1A a long range rifle, though it may be capable of longer range accuracy. I put a Burris 2.75 fixed power scout scope on mine.