In Pokémon Gameboy games, there are different types of Pokéballs. These differ in "quality" (with more costly balls, it's easier to catch tougher Pokémon - though my sister disagrees, and caught Mewtwo by freezing it and caught it using one cheap Pokéball...)

The following ball types are there in Pokemon Red & Blue:

Master ball is actually unique, but it is also the best type because it never misses and the captured Pokémon can't break out. If you want to make Mewtwo capturing boring and easy, this is your choice. =) You can get one from the SilphCo president once you rescue him.

Pokemon Gold & Silver has all of these, and in addition Kurt (in Azalea Town) can make these from apricorns:

  • Heavy ball for catching heavy Pokémon (Black apricorn)
  • Lure ball used when fishing (Blue)
  • Friend ball makes caught Pokémon friendly (Green)
  • Love ball for catching Pokémon of opposite gender of your active Pokémon (Pink)
  • Level ball for catching Pokémon of much lower level than your active Pokémon (Red)
  • Fast ball for catching fast Pokémon (White)
  • Moon ball for catching Pokémon that evolve via moon stone (Yellow)

(Source: Various game FAQs)

("Matkaan, Vulpix!")