Which are the major sects of Buddhism in Singapore? Which are these sects' main temples in Singapore?
According to Peter Harvey in An Introduction to Buddhism (second edition page 413)
43% of people in Singapore practice some form of Buddhism; mainly Chinese Mahayana but also some Thai Theravada or Japanese Soka Gakkai and more recently Tibetan Buddhism.
Hope that's of some interest.
There are Wikipedia articles for about 30 of the Buddhist temples in Singapore.