there actually is quite a lot...
i am not saying they are all best works though, but still worth the visit and look

check out
esplanade - dp architects (one of singapore's biggest firms) together with michael wilford & partners
one raffles quay - kpf
supreme court bldg - foster and partners
national library bldg - ken yeang
church of st. mary - woha
uob plaza - kenzo tange
raffles city - i.m. pei
assyafaah mosque - forum architects (this one on the cover of a+u magazine sometime before featuring trends in southeast asia)
the old old shophouses in chinatown
raffles hotel
the magnificent gopurams
changi airport
one george st - som
URA bldg n gallery (with a scale model of whole cbd area-very detailed)

thats all i can think of for now.. if there is somethin else ill post it later

thanks for the list, definitely post again if you think of more

paul rudolph has some high rise condos there i think

oh yeah paul rudolph got some stuff over there.. forgot the name.. its along beach road
and also check out bugis junction, as well as parkview square
there is a seminal design by william lim when he was still with DP architects.. but now its a dilapidated bldg... mile long complex i think..

also the indoor stadium by tange and vivocity by toyo ito