Ok, so maybe I'm biased. But in my daughter's opinion (the future paleontologist), the Kingfisher Illustrated Dinosaur Encyclopedia is the "best". And amazon has it on sale right now for an incredible price - less than $9!
Really, this encyclopedia covers way more than dinosaurs. It goes back to the Cambrian and Devonian periods and forward to the Pleistocene era and beyond. But I think they just use the word "dinosaurs" in the title because most people think all animals that lived "millions of years ago" were dinosaurs.
Now, of course, there is some evolutionary content sprinkled throughout. (Personally, I don't get too bent out of shape about books that mention evolution. I just use it as an opportunity to bring God into the discussion. But if you're sensitive about this issue, be aware.) Even so, this book is an awesome resource. You know a book is good when a kid has looked at it so much that the cover is all torn up.