Moving from the Ch'an Masters of ancient China to the 20th century, the mantles of the greatest Eastern teachers of self-realization arguably rest on the shoulders of Ramana Maharshi (birth name Venkataraman Aiyar, from Tamil Nadu, India; 1897-1950) and Nisargadatta Maharaj (birth name Maruti, from Maharashtra, India; 1897-1981). The teachings of both are well-known and easily available. There's no Easterner of the 21st century that I'm aware of who has joined their ranks.
In the West, there were three teachers I'm familiar with who I feel fit into the same category as Ramana and Nisargadatta: Franklin Merrell-Wolff (1887-1985), Douglas Harding (1909-2007) and Richard Rose (1917-2005). They are generally less well known than their Eastern counterparts, so I've assembled some details about them and their teaching on the Greatest Teachers pages of this site.
There are also pages on this site for four other 20th-century teachers I believe offer valuable resources and who are relatively unknown: J.J. van der Leeuw (published several books in the 1920s), Alfred Pulyan (1896-1966), Hubert Benoit (1904-1992), and William Samuel (1924-1996).
The current top teachers of self-realization I'm personally familiar with are all associated with the TAT Foundation, which Richard Rose founded in 1973. Several of Rose's students have carried their pursuit of self-definition to a successful conclusion ... the first three of whom, Bob Cergol, Shawn Nevins, and Bob Fergeson, I have provided some details on in the Ongoing Work page of the Greatest Teachers section of this site.
For another set of opinions, including suggestions on how to evaluate teachers or teachings you come across and some inspiring books and films you may have missed, check out SpiritualTeachers.org.