Robert Olah-Gal and Jozsef Sandor,  On trigonometric proofs of the Steiner-Lehmus theorem,
Forum Geometricorum, 9 (2009) 155--160.

Abstract: We offer a survey of some lesser known or new trigonometric proofs of the Steiner-Lehmus theorem. A new proof of a recent refined variant is also given.

[ps file] [pdf]