You are already doing the most important things, which are reading to him and reading in front of him every day. It also sounds like he is in just fine shape for kindergarten.
I think there are LOTS of games you could with him for fun that would help:
Find pictures of rhyming words (duck, truck, muck, pig, dig, etc) and print them out. Mix up about three sets and sort them into the right category. Google "word family activities" or "word family games" http://www.enchantedlearning.com/rhymes/wordfamilies/
Read nursery rhymes and poems with him and focus on the rhyme. Sing songs, listen to songs in the car.
Play site word bingo, or site word matching/memory using the Fry word list. I made bingo cards that have six words each. My son, who is 3, gets the same card each time until he seems familiar with the words, and then I get him another card. We make the dog, the baby, or the neighbors play with us. I show the card, say the word, and then give the card if he has it. When we are done, we count the cards he has won, and I give him a jelly bean, animal cracker, raisen, or whatever for each card he has. You could do something more systematic where you pick @ 10 words a week to work on - bingo, matching, spelling them with magnet letters, finding them in books, etc.
When you read with him work on his comprehension by making connections between the story and his life, helping him make connections (you have a dog, so does this boy!) , and by having him make predictions (What will happen next?) or draw inferences (Why did you think the did that?) or having him tell a sequel to the story.
PLEASE dont make him do a bunch of worksheets and workbooks.
Two websites I really like:
http://www.redshift.com/~bonajo/preschool_activities.htm
http://teachmama.com/
:)