I have a siamese mix who was best friends with my dog Barney.  She used to
follow him everywhere she'd even try to slip outside while the dogs went to
the bathroom.  Now that Barney has passed away she's just not herself.  I'm
hoping that in time she'll warm up to Lady our new dog but I'm not counting
on it.

Celeste

Both of my cats are/were better friends with my dogs than with each
other.  I had the cats first, then found my border collie mix, Tosh,
when the cats were 3 & 4 years old, and she bonded with both cats right
away.  Then I adopted Tessa, my Basenji Mix.  The cats often slept with
the dogs - never with each other. The dogs groomed the cats and vice
verse.   Mimi and Tosh slept with each other or next to each other
every night.  I chose to euthanize Tosh last Monday (due to illness),
and Mimi has been lost ever since.  I'm not sure she will ever get over
it - they were companions for 11 years.

-L.

I have read that they can become good friends with other species
(dogs, rabbits, etc) if they are socialized with that species early in
their life.

Justin

I used to work in a stable where a horse and cat were best friends.
They'd follow each other around, even playing tag in the corral, and
the cat would step carefully off the top of the stall and onto the
horse's back for naps.  I don't know how they met or how old they were,
though.

--
Jennifer

My cats and rats obviously love each other. I know this by the way the
rats try to kiss the cats when the cats sniff the rat cage. I mean, the
kissing is a bit vigorous, with leaping and a lot of Tooth Action, but
I figure this just shows the depth of their affection...

Steve.