For those that need a reference to a stamp catalogue that has details about Singapore stamps, I strongly recommend the Singapore Postage Stamps Catalogue that is published by CS Philatelic Agency. It is the only catalogue that I know about that deals solely with Singapore stamps.
The 2nd edition catalogue contains information about the Straits Settlements, Japanese Occupation, BMA and Issues till 2007. I am not sure whether the 3rd or 4th edition has been published. It retails for S$20 or US$24.
Good things about the Catalogue
The catalogue is very detailed and provides pictures of a comprehensive list of all Singapore stamps and even before Singapore gained its independence. It publishes the price of the various stamps and from it, you can find out lots of information like the number of stamps printed, the date of issue, number of stamps in a set, etc.
Bad Things about the Catalogue
The only misgivings I have about the catalogue is the haphazard arrangement of advertisements at both the front and back of the catalogue. Usually, advertisements should be kept to the back of the catalogue as I have to flip through various pages before I get to the front page of the catalogue.