I love looking at the early stages of a a creative work I've experienced in its finalised form. You get a glimpse of what-almost-was, what-could-have-been, and sometimes the thank-god-that-didn't-happen.
Bulbapedia has a fascinating page on prototype Pokemon and prototype trainers, as well as some Pokemon that just plain never made it into a Pokemon game. (Yet?)
Kurusu (left) and Honoguma (right) kind of look like Pikachu, in a different element type.
This is an early version of Gengar. It's not as cool as the actual Gengar that went into the game!
Girafarig without a butt is strangely cute.
D'aaaaw look at this early drawing of Charizaaaard.
Here is a female trainer who never got into the games. What was she meant to be? NPC? Protagonist? The world may never know.
Maybe you'll find these more pleasing than the actual Pokémon that Gamefreak created -- that is, if you're one of those crazy people who thinks Pokemon designs are getting worse.
Regardless, there's a bunch more at Bulbapedia that you should check out, including Slaking, Tyranitar and others. We've also covered a few early designs here.
Prototype Pokémon and characters [Bulbapedia]