I've been quoted a price for a new Armalite A2 $817 (good price?) and am about to buy my first AR but some on this board have suggested that I buy an A4. I want to be able to use both scope and iron sights without having to remove scope. Is there a way to mount an ACOG and iron sights to the rail and still use both, like you could with a handle mount?

Scope & irons w/o removing the scope?  ACOG on the handle is your best bet.  You could mount other scopes up there, but almost anything besides an ACOG will be too high.

I can't think of a way to mount an ACOG on a flattop that would let you use the irons w/o removing the scope.

Why do you not want to remove the scope?  If it's just concerns about return to zero, don't worry about it.  Mounts like the ARMS throw-lever ones, or the Armalite one-piece for regular scopes, will return to zero on reinstallation.  With a flip-up sight you'll just have one lever to throw to switch over.

Thanks Mike. You would prefer a flattop with the ARMS mount and an ACOG over a A2 with same scope? If that's the case, I may want to go the little extra distance and get the flattop  16" Colt with rail mounted sights & scope if I understand the available options correctly. Other opinions out there?

For a full size ACOG (like the NSN or the TA31s or TA11s) I'd say go with the flattop.

For the compact ACOGs I prefer them mounted on the carry handle.

In [b]my[/b] case, I want to be able to configure for irons or scope, but don't need both at the same time.  So I picked up a detachable handle from another board member for $80 and will get an ACOG as soon as I can afford it.  (In the meantime I've got a 4x I took off a .22 mounted in $8 rings with thumbscrews.)  Paper targets & soda cans won't shoot back while I switch sights so I don't care about speed on switching them and I'll save a little $ by just getting the thumbscrew mount from Trijicon (TA51 or TA60 depending on which ACOG I get).  

If I was concerned about speed of transitioning to the backup irons I'd probably go with an ARMS#19S throw-lever mount for the ACOG and either an ARMS or KAC flip-up rear sight.  Then I'd just have to flip the lever to pitch the ACOG, and flip the sight up to get back in action.  With that setup the scope and sight are at the same height.

If I was [i]really[/i] concerned about speed of transitioning I'd put a Compact ACOG on top of the carry handle so I could just drop my head a little to switch to the irons.  In that case the scope would be higher, but with a Compact ACOG it isn't too much.

It all depends on how quickly you want to be able to switch back and forth, and how much scope you need.  If you need more than 3x, the third option may not be the best.  If you need more than 3.5-5.5x the  second might not work either.  

If I didn't have the handle already I'd probably go with the second option, but I do kinda like being able to quickly dial in the 5-6 MOA of elevation to get the .22 kit zeroed, which I couldn't do with the flip-ups.