I was hesitant to even do this thread; there are so many 5.56mm rifles in the world today, much more than ten, which is the maximu number of choices.
You've got the Daewoos, and the Sigs, and the Beretta, and the new FN 2000, and the Japanese have their own rifle, as does Singapore, and that doesn't even get into the slew of 5.56mm AKs out there (select fire versions, even).
Of the ones listed, I think the G36K has a combination of features that I find the most appealing. I like what I see with the new FN 2000, as well.
True, my experience is limited to the M16A1 and A2, but that doesn't mean I think they're the coolest rifles out there. Not by a long shot...