Basic Psionics Handbook, but they seem a natural fit for a BX character class (and are already a playable race in newer game editions).
Click here to download the Dromite character class PDF.
Click here to buy the Basic Psionics Handbook at a special introductory price. (The price will go up when the print copies are released for sale in a little over a week).
Other additional psionic classes:
— The Devine
— The Savant
— The Sauteur