I like to think of Ciel as a grey Eevee (inspired by its GSC Shiny, but not "Shiny" per se since that would be too rare). Not the most cat-like Pokémon, but Game Freak staff have likened it to a cross between a cat and a dog. (Coincidentally, "puppy cat" is a nickname given to cats that exhibit dog-like behavior, such playing fetch and following their person around, traits exhibited by Ciel.)
I also considered Espurr, but it's more specifically based on a Scottish Fold. Glameow doesn't seem fluffy enough (depending on how one interprets the tail anyway: thin and springy vs wide and airy) and strikes me as more of a bi-color cat. Torracat could fit since it's got the 'chops and Ciel's technically a tabby (albeit diluted), but it doesn't remind me enough of him without giving it non-canon colors. Plus, Ciel loves to be packed around and that might be a bit harder to do with a Torracat... ^^'
Simon and Kiki would be Litten and Umbreon, respectively. These two are more family pets than "mine," but they're closer to being mine than our other pets.
Other "Pokémon" we have running around include a couple Meowth (calicos), Persian (Siamese mixes), and Purrloin (bi-color tabbies), a Sprigatito (lynx-point longhair), a few more Litten (tabbies) and another Umbreon (black cat), a Torracat (tabby tomcat), a couple Snubbull/Herdier/Electrike (was told they were Bostons but I think they're Buggs), and an outdoor Piloswine/Mamoswine (pot-bellied pig w/ tusks). Though things probably wouldn't have gotten this out of control if they were Pokémon, given their size, dietary needs, etc.
