IMO these are some of the best. It's a Romanian company that produces really good optics.
Here's the main site.
http://www.valdada.com/
Here's a CQB scope that would be great for a 16 inch AR-15. I love the reticle on this.
http://www.valdada.com/vn/ior/03k
And then here's another scope if you want a little more magnification.
http://www.valdada.com/vn/ior/03v
I actually like it a little bit better than the ACOG.
Then again, alot more people like the ACOG just because you see it in the news in Iraq.
They're both kind of expensive though ($800 to $900).
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This one is a little bit cheaper ($500) and it's a dot that doesn't run on batteries.
http://www.leupold.com/tactical/products/scopes/
It's only a 1X, but it would be great for close up.
I'm just not really sure what you want a scope for (specific use), so it's kind of hard to tell you pick one. You could be wanting to use it for three gun matches (in which case you'd probably want either a dot or a low magnification scope), you could be wanting to use it on prarie dogs and coyotes (in which case you'd probably want a high magnification scope) or you just might want it for general plinking.
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Or you could just get a 3X9X40 regular Nikon scope, those are pretty good for the money as well.
http://www.nikonusa.com/template.php?cat=4