Anything quirky, wierd, and intelligent in its own right:
Imps, Quasits, Nalgs*. You can never go wrong with divided loyalties personified in an eight pound bottle of bitter and mean.
Mephits - like above, just hellishly more annoying.
Pseudodragons - cute versions of the imp/quasit/nalg archetype. We've got one in my current campaign, and it's one of the few things keeping its PC master from going evil, which she's already inclined towards by virtue of her parents.
Faerie Dragons - the pipe dream of a chaotic good spellcaster, or a spellcaster with little tangible grip on reality. Insanely adorable, but also insanely dangerous since I give the little fellows a Wish 1/day.
Chaos Imps - mischief incarnate. Never ever allow a Xaositect tiefling wild mage access to one of these. You'll regret it.
*NE analogs to imps and quasits from somewhere back in the wee early years of Dragon mag, possibly before I was born, which I redefined in my games as yugoloth creations, much like guardian yugoloths are, used to tempt spellcasters to neutral evil and to allow the 'loths to get their claws into influencial people.