The first and the best is following.
Coins and Coinages of the Straits Settlements and British Malaya 1786-1951
Major Fred Pridmore
1968 2nd Edition
1st edition released 1955 didn't include Singapore merchant token.
It's the major update of 2nd edition.
Pridmore used 46 pages for detail description of tokens, which could not be found from any other book.
Pridmore revised his previous work in CBCN2 and used a different numbering system which seperated all major varieties, when CBCN2 number refers type only.
And also type defining, for example, CBCN2 Type2 (Island of Sumatra 'q' instead of 'p') was treated as a major variety of Type A/I (Variety 11).
Although this is the most accurate numbering system, few people use this. (maybe because the book is not a popular one, so sad...)
Plus, this is not a expensive book, usually realized $40-$80 when appeared in ebay.