The Medical (Therapy, Education and Research) Act (MTERA) is an opt-in scheme, where people can pledge their organs or any body parts for the purposes of transplant, education or research after they pass away.
Compare Human Organ Transplant Act (HOTA) with MTERA.

Anyone 18 years old and above can sign up as an organ pledger. A pledge can only be revoked by the organ pledger. Upon death, the organ pledger's decision will be respected, and his family members will not be able to revoke his pledge. You can choose to donate all your organs or specify those you wish to donate.
You can pledge your organs by completing the attached Organ Donation Pledge Form and sending it to the Organ Donor Registry.
http://www.moh.gov.sg/mohcorp/legislations.aspx?id=1674
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I have printed, persuaded both of my parents to be my witnesses, and will soon submit it.
My organs or any body parts shall serve the purposes of transplant, education or research after i'm dead.
My father is quite apathetic, and signed it immediately, but my mother took me some time to persuade.
I believe they are culturally taoist/buddhist, therefore it is easy for them to accept my body being cut-up. :D
Why waste my body parts when i'm not longer able to do good with them?
IMO, it is immoral to keep your rotting body parts while people dies/suffers without them.
Medical research on my body parts is gross, but contributes to saving thousands if not millions of lives.
This pledge should be an one way ticket to heaven.
If there is.