We have:
Topsy and Tim 'the new baby' - all about how Topsy and Tim's friend Tony has a new baby brother. Features the baby being breastfed (if that is important to you), having a bath, mentions how babies cry, big brother making him laugh etc.
My New Baby (Annie Kubler, Childs Play books): this is just a picture book with a little boy and the new baby. Again features breastfeeding, and shows the big brother helping/going for walks/having story time after baby asleep. Really lovely book to talk about with your LO as you can make up the story to go with each picture.
Miffy and the New Baby: not great - but if your ds likes miffy then okay!
Now we Have a Baby (lion publishing): This is my favourite - features two older siblings but mainly a big brother - a few excerpts below, 'here is a baby, newborn and tiny, there are lots of things to know about babies. Babies need to sleep a lot, you sometimes have to be quiet when baby is sleeping....everybody seems to love baby, sometimes you can feel left out....but every tiny baby is a little person who needs people to love them...love helps them learn about smiling and talking/helping and playing/caring and sharing (shows big bro playing with baby)...love makes baby part of our family for a family is love'
Its a really nice book!
I found that the books really helped my LOs get used to the arrival of their siblings. Good luck!