J., how much does your son already read? What is he interested in? That should be your guide for what books to get from the library.
When my son was a young pre-reader (reading pictures, not words in books) we sat together and read as much as I could - at least a few books everyday. We read a lot of Dr Seuss type books (Go Dog, Go! is not by Dr Seuss but is like it. Others were ABC and Green Eggs & Ham, Cat in the Hat, etc. Also Where The Wild Things Are, Max and Ruby books, (a lot of board books at this age, maybe your son still enjoys them or maybe he is a little past that) Berenstain Bears books are popular (and often teach a good story as well, so I love them as well) Clifford, and so many others.
Anyway, one thing I think that really helped him get started reading on his own is when we read together, after the story was familiar to him, I would pick out a word or name (something that is distinctive and easy to pick out at first. zoo or Max were good starter words, dog is a little harder until they know their letters really well. Anyway so we'd read (for example, Put Me In The Zoo, and pick out the word zoo) and I'd show him that word and tell him it was his word to read (this was all a game, not a quiz or you gotta do this type thing) and then we'd read and I'd point to the words as I read then when I came to "his" word (zoo in this example) then I paused until he "read" it and he enjoyed it.
Start easy (ie, just reading together) then add on (I started pointing to the words as we read since I wanted him to know that the black squiggles were words, where the story came from) and when he understands, move on (I started having him read one word that appeared often in the story and was easy to see/find/recognize) then moved on when it became easy to longer words/phrases (ie, Little Red Riding Hood was "his word" to read) then we move on to him reading a sentence or page then me reading a sentence/page in the easy books that were familiar to him, then on to books with more than several sentences on the page. Now he read chapter books on his own all the time (he is 7)
J., I would be happy to give you some more specific book suggestions when I know what his reading level is. I love to go to the library and I found a section there that has "easy reader" or "beginning reader" books (they are labeled level 1, 2, 3) and start with 1 if that's where your son is at. Check out a variety of books, some easier than the level he is at and some that are at his level to slightly challenge him. (Goal is not to overwhelm him and make him not enjoy reading. We adults enjoy reading books like Twilight and Harry Potter, etc that are middle school age level, so of course kids enjoy easy reading where it doesnt strain their brains. Still, give them some challenging interesting books too!)