I absolutely love Wit's End Teemo.Teemo
He's one of the few characters that has really worked well with the item both pre and post mana burn change.
I usually go 21 in defense with Teemo and a Wit's End/Bloodrazor core make him super tanky.
Can't decide if I like the mana regen yellows or flat armor more but I always stick with mr/level blues. I like the /level over flat mr because casters aren't too scary until they start scaling in levels, especially when you have 21 into defense.
I swap Wit's End out for Malady if the other team is light on magic damage though. I don't really like Malady as much, but I'm not sure there's much better in place of Wit's End in games where its weak.