I suppose someone should plug something by Bob Flexner given how influential he is online.
His original book, "Understanding Wood Finishing: How to Select and Apply the Right Finish". It's a great ground-up guide to wood prep, finishes and how to apply them. Look for the revised edition, this was originally published in 1994 so it was in need of updating when the 2nd edition came out.
His other book that's mentioned a lot is "Flexner on Finishing: Finally - Answers to Your Wood Finishing Fears & Frustrations" I've not read that one so don't really know what it's like inside, but it's sure to be clear and no-nonsense like all his writing.
Edit: if you're after the Hosker book mentioned by Phil there are two 1p copies of this listed on Amazon currently!
