A Writer's Toolkit
Essential books for creative writers.
The Art of PunctuationThe First Five Pages: a Writer's Guide for Staying out of the Rejection Pile (A Fireside book)Fowler's Modern English Usage (2nd Edition)
The Art of Punctuation
by Noah Lukeman
£10.99
Essential.
The First Five Pages: a Writer's Guide for ...
by Noah Lukeman

Very useful.
Fowler's Modern English Usage (2nd Edition)
by H.W. Fowler

Absolutely essential (if you're serious).
Concise Oxford English Dictionary: 11th edition revised 2008Roget's Thesaurus of English Words and Phrases: 150th Anniversary Edition11th Collegiate Dictionary (Merriam-Webster's Collegiate Dictionary (Laminated))
Concise Oxford English Dictionary: 11th edi...
by Oxford Dictionaries

Essential.
Roget's Thesaurus of English Words and Phra...
by Peter Roget
£22.75
Essential.
11th Collegiate Dictionary (Merriam-Webster...
by Merriam-Webster
£13.59
Essential.
Writers' and Artists' Yearbook 2009: A Directory for Writers, Artists, Playwrights, Designers, Illustrators and Photographers (Writers' & Artists' Yearbook)The Writer's Handbook 2009Correct English
Writers' and Artists' Yearbook 2009: A Dire...
by Kate Mosse (foreword)
£12.74
Essential if you want to sell your work.
The Writer's Handbook 2009

Essential if you want to sell your work.
Correct English
by John Ernest Metcalfe

Very good desk-side reference for those unsure moments.