Another interesting way, if you don't mind some texture (read: holes) in your cover stock, is to cut two flaps (one top, one bottom, each on one cover) running back to the spine ridge, and thread them through the slits in your booklet -- this one holds together pretty nicely for me!
It can save a bit of the cover sheet question, but does open up the "open tab space in cover" question. On the other hand, windows peeking into the insides have possibilities ~
