I currently have a stock LE6920, I have not decided on an optic yet, but in the meantime, I am looking for a rear backup sight.  Currently I am debating between wilson (around $110), yankee hill (around 80), and MI (60's?).  I am wondering if anyone has any input, I am probably going to do my shopping at brownells.  Also, does anybody know if the mako group drop in rails are any good?  I was looking at them because of their price (55 :D)

I really like the Larue BUIS on my 6920. Simple and bulletproof. I wouldn't use a folding BUIS unless I had to clear a magnified optic.

If you plan to put an optic on it eventually, the MI SPLP and the Troy are both good choices because they sit very low when folded and are unlikely to interfere with any scope you might put on it.
The Magpul MBUS is also worth looking at.  It doesn't sit as low as the Troy or MI but is half the price and is still a very good sight.
If you are looking for a fixed sight, there are some good choices(DD, Larue, Rock River, etc...)  but my favorite is the LMT.  It is Very solid and works like a standard A2.
Lots of good choices out there, just stay away from the low end cheap stuff, it will only frustrate you.
good luck
C