Pokemon
¤ Red and Blue
¤ Red and Green (Japanese)
¤ Blue Version (Japanese)
¤ Yellow Version
¤ Gold and Silver
¤ Crystal Version
¤ Ruby and Sapphire
¤ Emerald Version
¤ FireRed & LeafGreen
¤ Diamond and Pearl
¤ Platinum Version

Universal Information
¤ What is this section?
¤ Breeding Pokemon
¤ Evolution Methods
¤ Elemental Types
¤ Pokerus Infection
¤ Shiny Pokemon

Affiliates
¤ Amity Square
¤ Dark Eon Hideout
¤ Eevee's Headquarters
¤ Eevee's Mansion
¤ Jenviousity
¤ Lugia's Island
¤ Perfect Absolution
¤ Pokemon Battle Dome
¤ Pokemon Inferno
¤ Pokeshore
¤ PokeTech
¤ Pokeuniverse
¤ Pokemon Valley
¤ Sapphire Milotic
¤ The Spriting Shack

At the ruins of Alph, you need to solve 4 puzzles. Depending on which ones you solve, certain types Unown are unlocked. Once you complete all four, all 26 will be unlocked.

If you check three of them, you'll be confronted by one of the researchers. He'll upgrade your dex so they you can view what Unowns you have caught.