I recently came to know that schoolbuses no need to bid for COE.
http://www.lta.gov.sg/content/ltaweb/en/roads-and-motoring/owning-a-vehicle/costs-of-owning-a-vehicle/tax-structure-for-buses.html
Which other vehicles no need COE in Singapore?
List I know as below.
- School bus
- Omnibus (WTH is this?)
- Vintage cars on Classic plate scheme - Embassy cars - Some cars owned by disabled people (I have a friend who owns a lancer don't need COE) - Some vehicles of Voluntary Welfare Organisations (http://www.ncss.gov.sg/documents/COE%20Criteria-VWOs%20%28Apr%202014%29.pdf)
Add on more if you know!