My just turned 4 year old DS has a set of 4 like this, Discover the dinosaurs
Which he loves, we borrowed the plant eater one from the library and he wanted it renewed and renewed so we ended up buying it. They aren't cheap though, about £9-10ish each from Amazon marketplace. They do dinosaurs in the air, sea, meat eaters, plant eaters, prob about 12 dinos in each.
I got a good one in Asda with loads of dinosaur facts.
It has loads more info than the other more expensive ones he has and he likes it very much. It was only £2 in Asda too, so very reasonable. I nearly didn't get it for him because I thought it might be too old for him, but decided to get it anyway as only £2 and it was our bedtime reading for many nights. Has prob about 50 dinosaurs in and includes for each of them... their diet!
And also how to pronounce each name, where in the world they lived etc, which has got my son interested in that concept too.
We also have the Harry books, which are very nice, but they are obviously just stories, not dino facts.
I like the look of the one YouCantTeuchThis linked too, but I am not allowed to buy any more books 