Stanley Gibbons has Stamps of the World - it's a heavily simplified worldwide catalog (similar to Scott's) in 5 very large books. The country (or area specific) volumes are much more detailed.
And to correct Kirk's note about Michel, most of Michel catalogues are available in English as well these days. Michel's worldwide catalog consists of roughly 20 very heavy books.
And then there's Yvert & Tellier -
http://www.yvert.com/ - which is a french worldwide catalog.