Telepathy is an ability that allows a being to read the mind of another being. Certain hok'tar have shown telepathy, but this often requires genetic advancement or prolonged evolution.
History
Eggar was given telepathic abilities by Nirrti, as was Khalek by Anubis. (SG1: "Metamorphosis", "Prototype")
Adria, the leader of the Ori or "Orici" displayed this ability many times. (SG1: "The Shroud")
The Wraith also possess telepathy. They can only directly read the minds of their own species, but they can influence Humans. (SGA: "Rising", "The Gift")
When affected by a Ascension machine, Meredith Rodney McKay was able to read the current thoughts of people around him which led to an awkward moment between himself and Dr. Rafaela Esposito. (SGA: "Tao of Rodney")
Alternate realities
Todd from an alternate reality was able to get into John Sheppard's mind and even got his name. (SGA: "Vegas")