So, I just spent most of today introducing my cat to my girlfriend's cats, in preparation for moving in - basically, we really, really needed to make sure they could get along.
A bit of background: Her two cats have all their claws, and the big one (who's had his picture go up here before - he's HUGE) is a placid, friendly beast who is territorial about the neighbourhood cats and gets *very* angry about them getting near *his* windows.
The small one is high-strung and likes to play, rough.
My cat has never dealt with other cats. Dogs, yes, cats, no. She's okay with strange humans and strange dogs, but cats TERRIFY her. A neighbour brought over a kitten, once, and it saw my cat and wanted to play. My cat puffed up to three times her normal size and RAN to a high place where she could get her back to the wall and smack the shit out of the kitten if it tried to jump up after her. She didn't stop hissing and growling until a good hour after the kitten left.
Oh, and my cat has no claws. Zero. Don't even start with me on how it's cruel, I didn't do it. I got her from the Humane Society that way.
So, anyway, my biggest worries (that the big one would get territorial or the little one would decide to play) came completely to naught - both of them were curious about the newcomer, but kept all their body language totally non-hostile and kept their distance when my cat didn't want to talk to them.
This is good, because THIS is about as friendly as *she* got, all day:

It's a start.