I'd get one of the match sites from Bushmaster.  They have 3 sizes.  .052", .062", and .072".  I don't have a micrometer with me I don't know how big that is.  Any thoughts???  Thanks!

Edited:  What size comes standard on the Bushmaster?

I would guess the smallest one that you can see comfortably.  I have even heard of some people filing the front sight post to a point, but haven't tried it myself.

This is your first AR, yes?  Practice with the one you have before you go out and buy all sorts of gadgets you can live without.

.052 was a big help for me at 100 yard targets.
Filing down the A2 sight (or ordering one to try it on, since they're 8 bucks less) is not a bad idea either.  

The only downside to the National match sight is that it's not square, but a rectangle, meaning you lose one "click" of adjustability- instead of being able to rotate it 1/4 turn, it's really always a 1/2 or a full turn ( some sights are a trapezoid, so it's one full turn of the sight up or down for each adjustment), at 100 yards I'm guessing this means around 4" of adjustment for each click instead of around 2".

I would also like to know what the standard front sight post width is.  I too am without a micrometer.