Indulgences

1. Act of Family Consecration
2. Act of Dedication of the Human Race to Jesus Christ the King
3. Act of Reparation
4. Papal Blessing
5. Days Designated Universally for a Certain Religious Intention
6. Christian Doctrine
7. Eucharistic Adoration and Procession
8. Eucharistic and Spiritual Communion
9. Examination of Conscience and act of Contrition
10. Spiritual Exercises and Monthly Recollections
11. Week of Prayer for Christian Unity
12. At the Point of Death
13. In Memory of the Passion and Death of the Lord
14. Use of Articles of Devotion
15. Mental Prayer
16. Listening to Sacred Preaching
17. Prayers to the Blessed Virgin Mary
18. Prayers to one's Guardian Angel
19. Prayers in honor of St. Joseph
20. Payers in Honor of the Apostles Peter and Paul
21. Prayers in Honor of the Saints and Blesseds
22. Novenas, Litanies, and the Little Offices
23. Payers of the Eastern Churches
24. Prayers for Benefactors
25. Prayers for Pastors
26. Prayers for Supplication and Acts of Thanksgiving
27. A priest's First Mass and Jubilee Celebrations of Ordination
28. Profession of Faith and Acts of the Theological Virtues
29. For the Faithful Departed
30. Reading of Sacred Scripture
31. A Diocesan Synod
32. A Pastoral Visit
33. Visiting Sacred Places

*From the Manual of Indulgences

To acquire a plenary indulgence it is necessary to perform the work to which the indulgence is attached , as well as fulfill the conditions below; or if the prescribed conditions are not fulfilled, the indulgence will be only partial.

1. That the person truly repudiate and be sorry for all sin, mortal and venial
2. Reception of Holy Communion on the day the indulgence is sought
3. Sacrament of Penance several days (within 20) before or after the indulgence is sought
4. Prayer (which can in the form of an Our Father and a Hail Mary) for the intentions of the pope on the day the indulgence is sought

Only one plenary indulgence per day can be obtained (unless it is the hour of death). Several plenary indulgences may be gained on the basis of a single sacramental confession; only one may be gained, however, on the basis of a single Holy Communion and prayer for the pope’s intentions.

You can gain an indulgence for someone in Purgatory. The month of November is dedicated to the souls in Purgatory. During this month, Catholics are especially urged to gain indulgences for the Poor Souls in Purgatory.

Further reading

Indulgences at New Advent
Myths about Indulgences at Catholic Answers