There is an interesting occurence where certain spiritual
practitioners who attained advanced level of realisation dissolving
their bodies into light at death or even transcending physical
death.
From my findings there are practitioners from Buddhism, Bon and
Taoism who attained this kind of realisation.. however there may be
others from other traditions as well... but I could not
ascertain.
In the Tibetan traditions, Rainbow Body attainers can be from
Bon or Buddhist Dzogchen strand of Practitioners. According to my
finding, the Bon strand of Dzogchen originated from an Enlightened
Being that predated the current era of Buddhism. It is said that
the Bon Dzogchen is at least 15 000 years old.
In Taoism, there is sparodic accounts of Rainbow body occurence
as well. In fact, there is a mountain in China that is named after
such a person where his body dissappeared.
Here are useful and interesting links related to this amazing
subject:
http://www.rigpawiki.org/index.php?title=Rainbow_body
http://www.berzinarchives.com/web/en/archives/advanced/dzogchen/basic_points/introduction_dzogchen.html
http://www.rigpawiki.org/index.php?title=Garab_Dorje
Recent Rainbow Body Attainers
http://www.rigpawiki.org/index.php?title=Khenchen_Tsewang_Rigdzin
http://www.rigpawiki.org/index.php?title=Khenpo_Ach%C3%B6
http://yachenlama.com/?page_id=1005