This is an old paper, but it is surprisingly little-known: Pseudogenes: Are They “Junk” or Functional DNA?. It’s a review paper of pseudogene function.
My favorite example in the paper is the antigenic variation. Essentially, the pseudogenes store alternative configurations of parts of genes. The organism can quickly reconfigure itself by swapping various parts in and out of pseudogenes. Many species have been found with this ability.
Pseudogenes used to be thought of as the ultimate example of “junk DNA” – something that we *KNOW* that was functionless. But, it turns out, pseudogenes continue to provide more and more evidence of function, much of it being part of directed mutation – something else that the Darwin lobby said couldn’t happen.