Summonable Protoss minions comprehensive list:
All Protoss classes (mage, rogue, druid, priest):
Zealot (from Chrono boost and Artanis)
Void Rays
Mage:
Colossus
Rogue:
High Templar (summons archon if two in board)
Dark Templar (summons archon if two in board)
Druid:
Immortal
Carrier (summons 4x interceptors each turn)
Priest:
Sentry
Mothership
If aiming to summon the most protoss minions possible, I recommend going with a priest mothership deck, as creation protocol /synchronize can make extra copies of the only cheap protoss minion (sentry). They also get a spell that summons a copy of a protoss minion (Hallucination), and Mothership creates up to 4 extra protoss minions between its battlecry and deathrattle.