Not technical writing, but the best book I've ever read on writing (including Elements of Style etc.) is "Getting Published in International Journals: Writing S

Not technical writing, but the best book I've ever read on writing (including Elements of Style etc.) is "Getting Published in International Journals: Writing Strategies for European Social Scientists". On the surface it's aimed at academics who are non-native speakers of English, but in my experience most people could do with reading it.