This is a true favorite in our house right now. I think we read it about at least 4 times each day and it never seems to get old! I like the repetition because, my toddler caught on pretty quickly. She can "read" this book all by herself by looking at the pictures and it's adorable to watch/listen.
Here is a nice little video of the author, Bill Martin, Jr.,
If you do a search for Brown Bear, Brown Bear, you'll find lots of activities and lessons. Other related books are:
Panda Bear, Panda Bear, What do you See?
Polar Bear, Polar Bear, What do you See?