IMO, I found your list to be extremely biased, considering you seemed to mention your own mod (BTB's game improvements) as somehow related to the usefulness of every other mod on the list.
I believe a thread like this is supposed to be biased. The question was "What are YOUR essential mods", not "What are the best mods of all time in your unbiased opinion".
I never play without my http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7166 anymore. I had one character who slogged it through the Main Quest without any mods at all. Since then, a teleport ring is a must-have, and since I made this one, it's adapted to my taste. Some kind of head replacer is also essential to me, usually Better Heads. Finally, I won't play without my http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7335. I made it because I got tired of mixing up my enchanted items - all the icons were the same. Now it's easy to tell the difference between them.
Also, Tamriel Rebuilt - awesome. The rest of my mods are subject to change.