I made these as gifts for some friends. I used a 1.5mm crochet hook and the equivalent sized yarn. At 2.4cm (or 3cm including tail) these tiny cats were the perfect size for attaching to a mobile/cellphone or key ring. Although not in the pattern, I also crocheted a length of chain stitches to use as the strap and ran it through the body and secured it at the bottom.
They are so adorably tiny!
The pattern I used was from “Amigurumi Cats and Friends”. It is available in many places on the internet. The book itself is in Japanese, but don’t let that put you off – I can’t read Japanese and I managed! 
Like many Japanese patterns, all the stitches are written in international crochet symbols which are easy to follow. And there are lots of diagrams and sketches to guide you through assembly.
Just a Note: If you are new to Amigurumi, there’s a great guide here. And if you are new to international crochet symbols, there’s a great post here about how to read Japanese patterns and what the international crochet symbols mean.
And finally, here’s a photo of the cover of the book for your reference. 
Happy Crocheting!
cleo
July 20, 2011 at 5:17 pm
this is a fantastic book – I have it!!
dominiquemitchell2012
February 20, 2013 at 4:52 am
these are sooo cute! Im useless at making teeny tiny things! I might have to try this one though, irresistible!