DigimonWiki:Digivolution References/Adventure:

"Tokyo Digital Crisis" [01]
 * Koromon > Agumon > Greymon
 * Argomon (Fresh) > Argomon (In-Training) > Argomon (Rookie) > Argomon (Champion)

"War Game" [02]
 * Argomon (Champion) > Argomon (Ultimate) > Argomon (Mega)
 * Greymon + Garurumon > Omnimon

"Birdramon Soars" [04]
 * Botamon > Koromon
 * Biyomon > Birdramon

"The Holy Digimon" [05]
 * Tentomon > Kabuterimon

"The Targeted Kingdom" [06]
 * Palmon > Togemon

"That Boy is Joe Kido" [07]
 * Gomamon > Ikkakumon

"The Children's Attack on the Fortress" [08]
 * Punimon > Tsunomon > Gabumon

"The Steel-Solid Super Digivolution" [10]
 * Greymon > MetalGreymon (Vaccine)

"The Wolf Standing Atop the Desert" [11]
 * Garurumon > WereGarurumon

"Lillymon Blooms" [12]
 * Togemon > Lillymon

"Garudamon of the Crimson Wings" [13]
 * Birdramon > Garudamon

"The Kings of the Insects Clash" [14]
 * Kabuterimon > MegaKabuterimon (Red)

"Zudomon's Iron Hammer of Lightning" [15]
 * Ikkakumon > Zudomon

"The Jet-Black Shadow Invades Tokyo" [16]
 * Eyesmon Scatter Mode > Eyesmon > Orochimon

"Countdown to Tokyo's Annihilation" [18]
 * Orochimon > Nidhoggmon