My 18 year old tom-cat adores, and is adored by our 17 year old queen (half his size, twice the attitude... and the 18 year old has more than enough of that to power a small village, himself!). They regularly curl up together, groom each other, and now that the 18 year old is losing his marbles somewhat (he sits in the bath during the small hours of a morning and yodels loudly - because the acoustics mean the sound carries - until someone yells where they are, at which point he'll pootle off and sleep on top of their heads until the alarms go off! He was diagnosed as having feline dementia maybe 4 or 5 years ago, but he's happy - until the middle of the night, when he forgets how to find one of us!) the queen will follow him around and make sure he's okay.
Our 10 year old cat, however, is a complete loner. To the point where, if you suggest that he might like to interact with someone/another of his own species, he gives the most withering of looks, which sort of suggests that you'd asked him to put the bins out, or something.
Our 8 year old cat, meanwhile, is in love with our 9 year old dog. Seriously in love with. The poor dog cannot go for more than half a day without the cat trying to groom him, present himself, lie on top of him, curl up on top of his head, generally flirt with him... and the dog is more than a little terrified by the attention. The love affair is a new "thing", though. Only started happening about a year ago. And whilst it's fairly amusing to watch unfold, I do feel quite sorry for the (thankfully a complete wuss who is healthily terrified of the cats and their machinations) dog. Because if he doesn't flirt back, then the 8 year old will smack him about his chops and stalk off in a strop... until all is forgiven and the dog is the best thing ever again!
The 10 year old cat gets on quite well with the 18 and 17 year old cats, and seems to enjoy tormenting the dog (will sit by food bowls with three chunks of cat-meat in, just watching the dog squirm in pleading anticipation... until one of us moves him!). The 8 year old cat doesn't even feature on the 10 year old's radar. The 8 year old cat is tolerated by the 18 and 17 year old cats (although if he's still hungry, they'll step back and let him finish their food out of their bowls, I've noticed, so there's some sort of affection there).
Apart from the 8 year old cat, the dog is so far beneath feline contempt that he's a non-entity... but the dog's best friend is my 11 year old DS, so it all works out in the end.