I've had many playthroughs so I don't remember all of them, would probably fill 2 boxes
Most notable ones were: Metagross, Milotic, Slaking, Gardevoir, Gallade, Flygon, Garchomp, Ninetales-A, Electivire, Gyarados, Tyranitar, Galvantula, Cofragrigus. These guys were mostly in the main roster, with others coming in and out.
My starters were Torterra, Infernape, Primarina and Blaziken (wouldn't accept to use another starter even if I got it later in the game, gotta show loyalty to my first partner!)