Barnabus will head-butt (HARD)
Smokie will move her head to one side and give a rub
Leonidas will just stare (but he ducks when you go to pet his head)
Jebediah will head-butt
Marley will sorta duck, then squeak and head-butt my chin
Smeagol will head-butt or tilt and rub one side (depending on his
mood)
Pandora just smiles with her eyes closed (then she'll open an eye if I
don't head-butt her)

Smokie Darling (Annie)

The cats that have tolerated that much contact have allowed and even seemed
to get a kick out of it when we initiate headbutting.

But the attitude has to be right.  Eyes down, no eye contact and gently lead
with the upper forehead.  Even Molly will allow a headbutt once in a blue
moon and she doesn't really like to be touched.

Except of course by Steven.  She adores that kid.

Jo

Betty headbutts hands and chin, but won't headbutt a person's head.
She'll sort of sit there and patiently accept being nudged.

They're all different, I guess.  Stinky has always been a tête-à-tête
man. ;)  Dante will duck if you come in at his head, but he will come
to me on his own if not pursued..  

Theresa
Stinky Pictures: http://community.webshots.com/album/125591586JWEFwh

Make Levees, Not War

Miranda doesn't like my face to come too close to hers. Nikki was the same.

But Caliban headbutts me all the time. If I see him sitting somewhere at
a suitable height, I go towards him making kissy sounds, and he squints
and stretches his head towards me for a headbutt. He also gets into my
lap to headbutt me.

Baggy hated me putting my face near his when he first lived here, after a
while when he realised it was a friendly gesture he started purring and
doing the same.

Tygra tolerates and sometimes even likes being headbutted by me,
she'll give me kisses (licks) on my lips as well.  Possum loves to
headbutt other parts of my body (especially my boobs) but isn't keen
on face to face contact. It's just as well really, seeing as i'm
allergic to them, my nose gets stuffy and my eyes get runny with too
much face to kitty contact.

Kristy

mine go both ways, Quinn and Harry are both leery of head-to-head closeness,
Bosco (RB) used to love it, to point of distraction at night in bed (not great
having a cat want to sleep on your head, Siamese loved all and  any contact.
Quinn loves to head butt my legs esp. when he feels that feeding time is
overdue.

my Tortie,Maggie,backs away from me....but my Tuxedo LOOOOOOVES it,Oreo
headbutts me right back,sometimes pretty hard!