I had a player in my campaign ask to have a pseudodragon familiar as an Improved Familiar. I thought it was important to make it seem different than a regular familiar, so I created Farrah the pseudodragon as an NPC.
I have to tell you, this is one of the most fun things I've done in the entire campaign.
The party ran into Farrah in a random wilderness encounter (she had been treed by a couple of dire wolverines who had damaged her wings enough that she couldn't fly away). The party heard these little telepathic cries of help and responded. Then the sorceror who wanted the pseudodragon went *nuts* trying to win the thing over. Farrah knew a good deal when she saw one, and she basically wrapped the sorceror around her little finger. Farrah was getting magic items, special rings custom made for her (nonmagical, but still), all the spiders and nuts she could eat, etc.
AND the party has used Farrah's telepathy and whatnot to good effect. (Too long to go into here.) Though, since Farrah is a little impulsive and eager-to-please, sometimes things don't quite turn out the way the party wants ...
Anyway, once Farrah and the sorceror officially bonded as familiar's, I offered to let the PC have control of her. My entire party, bless their hearts, insisted that I continue to play her as an NPC (though she took orders from the sorceror pretty well) because they loved the way I played her.
Unfortunately, now the sorceror is leaving the party (the player is just too busy to stay in the campaign), and the wizard in the party doesn't want a familiar because he doesn't want to have to worry about it getting killed.
Long answer to a short question ...