One of the first things I needed to do as a freelancer was to stock my bookshelves with reference material. I did buy a few books – The Editor’s Companion; the Style Manual for Authors, Editors and Printers; The Australian Editing Handbook; and The Design Manual. They look nice on my shelves and make me feel like a serious editor, but they were fairly expensive and I rarely use them (partly because doing so would mean moving out of my chair and reaching over to them, which I find myself reluctant to do while I’m working).
I also bought a couple of subscriptions – The Chicago Manual of Style Online (CMOS) and the Macquarie Dictionary and Thesaurus Online. Both of these were much cheaper than any of the books I purchased, and I’m finding that I actually use them, probably because I can do so without getting up from my chair. I particularly like the CMOS, because they send regular emails with new questions and answers that have been added to their website (although I hate the fact that they write ‘website’ as two words, with a capital W!).