[1] http://www.amazon.com/Modern-Technical-Writing-Introduction-...
HN discussion from almost a year ago: https://news.ycombinator.com/item?id=8699178
Related: http://docs.writethedocs.org/
Word Up! by Marcia Riefer Johnston (http://www.amazon.ca/Write-Powerful-Sentences-Paragraphs-Eve...) is also solid for improving the quality of your writing. The book itself is a bit… precious, though.
How to make sense of any mess by Abby Covert is great for organizing (which is a big part of tech writing for me). Available on Amazon and now also at http://www.howtomakesenseofanymess.com/
* Chicago Manual of Style
* NASA Technical Report Writing (Technical Memorandum 105419 (1))
(1) A personal favorite: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/1993001...
http://chronicle.com/article/50-Years-of-Stupid-Grammar/2549...
I'm on a device with a glass interface so it's too difficult to get the link, but you can just google it.