Besides a person's wedding and Yom Kippur are there any other events which provide someone with atonement just by dint of the occasion itself?
Becoming king causes one's sins to be forgiven (Yerushalmi Bikurim 11b)
The Gemara (Sanhedrin 14a) states that assuming certain positions of authority (the Gemara there is discussing semicha, but says it's also true about anyone who is "oleh lgedulah") causes one's sins to be forgiven (See Maharsha, however, for an alternate understanding of the Gemara).
Converting to Judaism causes one's prior sins to be forgiven (Yerushalmi Bikurim 11b).
death and getting killed by bais din
death atones as [Isaiah 22:14] states: "It was revealed in my ears [by] the Lord of Hosts, surely this iniquity will not be atoned for until you die."