I like the Catsan one with the kitten just cos I think it's cute!
I also remember liking the Walls ad with "Look! Cat!" - I shouted that particular phrase out a lot then (usually I'd associate it with the cat smilie on MSN and say it at the most random moments!), and also the Knorr pandas (especially "That smells belting!")
I could go on all day with TV ad catchphrases!
