Our five-year-old is learning to read, and after looking at a lot of the early reader series, we found the Brand New Readers series published by Candlewick Press.  Each book features a animal character, like Worm and Mouse, and tells a story with a simple sentence on each page, accompanied by bright and colorful illustrations which assist in telling the story.  There are also helpful reading tips for parents.  Because the books are easy to use, they encourage more reading.  My daughter is now comfortable reading them alone or with friends.  I bought mine at Barnes and Noble, but they are also available on Amazon.