How about a joke book?
Dd has quite a few joke books and gets endless pleasure from reading them aloud to anyone who is prepared to listen.
Also we really enjoy reading the Dr Seuss books aloud to each other.
You really have to concentrate as a lot of them are quite tongue-twisterish.
How about asking him to read you a bedtime story.? Sometimes I lie on dd's bed with my eyes closed and she reads to me.
A favourite, that is brilliant for reading aloud is is "Bubble Trouble" by Margaret Mahy. You really have to concentrate and enunciate.
"Little Mabel blew a bubble and it caused a lot of trouble...
Such a lot of bubble trouble in a bibble-bobble way.
For it broke away from Mabel as it bobbed across the table,
Where it bobbled over Baby, and it wafted him away.
The baby didn't quibble. He began to smile and dribble,
For he liked the wibble-wobble of the bubble in the air.
But Mabel ran for cover as the bubble bobbed above her,
And she shouted out for Mother who was putting up her hair.
At the sudden cry of trouble, Mother took off at the double,
For the squealing left her reeling...made her terrified and tense,
Saw the bubble for a minute, with the baby bobbing in it,
As it bibbled by the letter-box and bobbed across the fence.
On her garden Chrysta Gribble had begun to cry and cavil
At her lazy brother, Greville, reading novels in his bed.
But she bellowed, "Gracious Greville!" and she grovelled on the gravel,
When the baby in the bubble bibble-bobbled overhead"
and it goes on for another 15 verses.
Sorry, probably no good for a four year old, but it is brilliant .