This is a question we come across quite often when collectors of Cyprus stamps contact us for our free crib sheet (an excel list of all stamps issued since 1880 up to the most current catalogue issue). Our recommendations are here below:
For stamp listings displayed on Cyprus Stamps website we use Stanley Gibbons catalogue numbers (SG reference). This is a UK published catalogue which is issued approximately every 2 years around the month of November. The last edition published was in 2011 and as in the previous issues it contains Cyprus, Malta and Gibraltar stamp listings.
Tip: We find this catalogue is usually a little cheaper to purchase on eBay and depending how you are looking to value or complete your collection you may find it's not always necessary to have the most up to date catalogue. You should find that older versions can be purchased at very reasonable prices.
In Cyprus, you should be able to purchase the Hermes St. Frangoudis (a Greek published catalogue) who also have their own numbering/catalogue reference system for stamp issues and we're not familiar with any other stamp dealers who use these numbers. However, it does also list the prices for First Day Covers (FDCs) and provides good images of every stamp issue, which the other catalogues do not.
Tip: If you are a collector of Cyprus FDCs as well as stamps we would suggest this is a handy book to have simply as a reference guide.
The most commonly used catalogue reference systems used on the internet and stamp auctions are: Stanley Gibbons, Scott (USA catalogue) and Michel (German).