Ha. I'll second (or fourth?) P.D. Eastman. Go, Dog Go! was one of DD's favorites at around the time she started reading. In fact, it was the book she used to first demonstrate that she had sight words. I bought it because we were out running errands all day, I forgot to bring something for DD to do in the car, and it was the best thing I could find at the used bookstore we stopped at. DD fell instantly in love with it.
Other than that, DD really didn't get into any of the very simple early readers. Once you get past that stage, there are some great early chapter books (e.g., Frog & Toad, Fly Guy, Amanda Pig, etc.) that I still enjoy to this day.
