One advice/recommendation - some ATMs might display an offer to use currency conversion rate offered by that ATM or post charges directly using card's currency. DO NOT accept such offers - it is basically DCC and will end for you being charged 3-7% on top of the interbank exchange rate.
Three main local banks in Singapore are DBS, UOB and OCBC. You can find their ATMs pretty much anywhere. Any shopping center will have at least one ATM from each of these banks, usually stacked together.