There's an interesting piece at The National about one of the more amazing works of the British imperial era in the Middle East, John Gordon Lorimer's Gazeteer of the Persian Gulf, Oman and Central Arabia. As the article notes, the project was originally classified and intended as a handbook to the region as Britain was consolidating its power there. It grew to be a six-volume, 5000 page encyclopedic survey of the history, geography, tribal structure and topography of the Gulf and its hinterlands, complete with maps and genealogical charts of the ruling families. It is the starting point for almost any historian working on the Gulf prior to the 20th century. You can find a listing of its contents here, in a prospectus for a library reprint edition.
Sadly, in an era when so many pre-1923 works are available online, only one of the six volumes actually seems to be available, the fifth (which is called volume IIa confusingly enough), and which is the first half of the "Geograpical and Statistical" gazeteer, and is available on Google books. Browsing through it will give you a taste of the whole, and most decent Middle East libraries should have a set.
I'm glad The National thought to write about it since it's one of those works I've used but don't own myself (the reprints are pricey) and might never have thought to blog about.