Catholic
Protestant
Presbyterian
Lutheran
Baptist
Methodist
Jesuit
Jehovah's Witness
Greek Orthodox
Orthodox Jew
Reconstructionist
Karaite
Humanistic
Alternative Jew
Sunni (all divisions)
Shi'a (all divisions)
Kharijite (all divisions)
Sufi (all divisions)
Mu'tazili
Ash'ari
Maturidi
Athari
Murjite
Vaishnava
Śaivite
Shakta
Smartha
Bhakti
Jain
Hinayana
Mahayana
Vajrayana
Neo-Druid
Dievturi
Ásatrú (I have no idea what a worshiper is called)
Theodist
Hellenism (again, no idea what a worshiper is called)
Jewitch
Kemetism (ditto)
Wiccan
Spiritual Satanist
Golden Dawn member
Scientologist
Taoist
That's a bit long. And it's skipping over the Sunni/Shi'a/Kharijite/Sufi divisions, and the slightly more obscure Christian denominations, and a couple Jewish divisions, and I haven't even touched on the traditional Asiatic religions (aside from Taoism, which I just remembered and tacked on at the end. And Bhuddism, if you think it falls into that category).
Yes, it could probably be compacted significantly. But a Protestant would hate getting thrown into the same group as a Catholic, and let's not even mention the relations between the various Muslim divisions. And I daresay a Wiccan will be quite different from a member of the Hellenic Polytheistic Reconstruction.
And it leaves out agnostics, atheists, and the unsure, but that's only because I just now remembered them. And Zoroastrianism, which has a few subdivisions of its own. And Sikhism.
So you have to choose how far you want to generalize religion.