For collectors wanting a good general catalogue of all the world's stamps you can't go past Stamps of the World - clear listings, good scans, sound pricing etc. (getting free airmail postage to Australia was an added bonus - thanks Amazon!).
However, this is spoilt by the errors and inconsistencies. Those I noticed within a few minutes were:
* Self-adhesives for GB and Australia are listed for some issues, and not for others, leaving the user unaware of the catalogue pricing of these, and their catalogue numbers. There seems to be no logic behind why some are listed and others are not, and should be fixed for the next edition.
* Miniature sheet listings sometimes contain errors where the value of the stamps is not given.
* The listings for Great Britain includes modern stamps which only differ by perforation, watermark or printing process. However, due to the simplified nature of the catalogue this significant information is removed, leaving the reader unaware of the difference between these stamps, and their prices. It would've been better to remove these stamps entirely from the listing and avoid non-specialist collectors trying to work out whether they have a stamp catalogued at £2 or £20.
I am also disappointed that SG lists a set of stamps under Haiti, which have been deemed to be bogus by the Haitian authorities (see The Haiti Philatelic Society website).