The Elephant & Piggie series, by Mo Willems.

IMHO, the best kids book we've encountered. Some of the nice features:

a) well drawn and sharply delineated characters. (One of my pet peeves about some kids books is difficult to distinguish images that tend to get lost in a sea of bright colors.)

b) the text is _large_ and changes size according to the emotions of the characters.

c) phrases are repeated -- great for language acquisition -- but not in a way that's irritating or vacuous.

d) funny stories; real emotions that toddlers can grok.

e) good construction -- high quality printing, thick pages, etc...