Well, here's my two cents. Most of these are personal favorites, though it's always hard to really choose
Rodent: Zigzagoon
Bird: Pidgey
Bug - nice looking: Butterfree
Bug - Poison: Scoliopede
Starters:
Grass: Bulbasaur, Treecko, Snivy (especially if it'll become a Dragon

)
Fire: Charmander, Cyndaquil, Tepig
Water: Squirtle, Totodile, Oshawott
Legendary sets: Bird Trio, Regis(all four), Latios & Latias, Weather trio
Legendays(Chibi): Mew, Celebi, Jirachi, Victini
Legendarys(major): Kyogre, Groudon, Rayquaza, Zekrom, Reshiram, Kyurem
Legendarys(other): Deoxys, Darkrai, Arceus, Genesect
Also, if you're looking to add unique ones, I'd suggest the mythical "Grandfather" evolutions of the starters, at least some of the originals. If you're not familiar with it, when I was a kid I lived in japan, and there was this special set of concept artwork (I think it was anyway) that you could get with a special book back during the first generation. Nothing ever came of it, but there were new evolutions beyond the original three for the starters; at least, that's what it looked like. Charizard evolved into a three headed version of itself, Venusaur evolved into a version of with three trees on it's back with a spearow among the leaves, and Blastoise with four cannons, rather than two, which were in pairs. These were referred to as the Grandfather pokemon, and this was about 16 years ago, so nobody seems to remember but me and a few others. I think it would be awesome if you could include those. Just a suggestion.