I really enjoyed Writing with Style. It's focused on process rather than rules (a la Strunk & White): how you should think (and how professional writers think) about the audience while writing and how to structure your text to best get your point across.
Writing with Style is great. It's not about thesis writing specifically, but is focused on how professional authors think about their audience when they write. It's enjoyable and useful.
I found "Writing with style" excellent. It focuses on the thought process of writers: how to think from your audience's point of view, how to edit, and how to structure your writing in a way that communicates your point well.