Base Set through Team Rocket:
Bill
Computer Search
Ditto (Fossil)
Double Colorless Energy
Energy Removal
Goop Gas Attack
Gust of Wind
Item Finder
Nightly Garbage Run
Pokémon Trader
Professor Oak
Scyther (Jungle)
Super Energy Removal
Bill is debated, Energy Removal and Super Energy Removal are sometimes used together, sometimes used one or the other, and Pokémon Trader was only used in decks that really needed to get a specific Pokémont at a specific time: crowded Potpourri decks, Stage 2 decks, etc. Goop Gas Attack might be a personal preference thing. Some archetypes had staples that would add to this list: Pokémon Breeder was a must for Stage 2 decks, Pokémon Center was a must for Raindance decks, and PlusPower was a must for Haymaker decks. Lass, Scoop Up, and Switch were also strong, common plays, but not universal.