This is a list of dungeons you can access as a free to play member.
Immirian Ravine (40+ set at the level of the first person to enter)
Frost Swamps (40+ set at the level of the first person to enter)
Oasis of Zahara (40+ set at the level of the first person to enter)
Toirdealbach's Tomb (46-48)
Dead Mans Hand (solo, 50+ set at your level when you enter)
Catacombs (55-60)
Isle of Iron Statues (solo, 80)
Onyx Chambers (80)
Atzles Fort (80)
Ardashir Fort (80)
Kylikki's Crypt (raid)
Yakmars Cave (raid)