So which drow book to get? Plot and Poison, Sheloth, The Quintessential Drow, City of the Spider Queen, The Complete Guide to Drow... which one is worth it?
For what purpose. You have adventures, setting supplements, and rules supplements mixed up there.
For supplements, Plot & Poison is and awesome book with lots of twisted ideas. Quint Drow I would put second; it has some twisted ideas of its own like limbgrafting, rules for seduction, etc. Complete Guide to Drow is full of munchkinistic rules that you should avoid, but it does have some stuff that could be useful (if, for example, you adore the idea of old style drow weapons that decay in the sunlight...)
For setting supplements, Sheoloth is obviously your only choice. The city is decent, but the NPC stat blocks have serious issues.
For adventures, CotSQ struck me as a "Death by perpetual encounter" sort of adventure, but it has lots of well done encounters. An enterprising DM could make good use of this book by adding some plot depth and interaction or subterfuge possibilities. Queen of Lies, pretty much the same deal, but as it is a bit thinner, it might actually be more tolerable if you chose to run it in "wade through the bad guys" mode.