Edward R. Tufte: 'The Visual Display of Quantitative Information'. The Graphics Press (USA), Cheshire Connecticut, 1993. All of Tufte's books are as beautiful as they are excellent, but this is his best.
Buy this book at Amazon.co.uk

A.S.C. Ehrenberg: 'A Primer in Data Reduction'. Wiley-Blackfield, London 1982. Practical advice on presenting data from the master. Beautifully written.
This book is currently out of print, but second hand copies are available at a reasonable price from Amazon.

Robin Williams: 'The Non-Designers' Design Book', Peachpit Press, 1994. Sensible advice on presenting general information in a book designed for the "visual novice".
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Schriver, Karen A. 'Dynamics in Document Design', John Wiley & Sons Inc., 1997. This large (592 pages) text book covers the wider issue of presenting text. Very thorough with much food for thought, even for non-typographers.
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BS7581:1992 Guide to the Presentation of Tables & Graphs published by the British Standards Institute. This is a first rate, succinct (24 pages) and lucid document, setting out sound advice simply. However at £130 (US$ 214) per copy [May 2011] the cost is prohibitive. Available from:
http://shop.bsigroup.com/en/ProductDetail/?pid=000000000000285987
[Please feel free to complain about the extortionate price to the British Standards Institute.]