For beginners:

The Interpet Encyclopedia of The Marine Aquarium
by Dick Mills [Salamander 1987]
ISBN 0 86101 306 9

Latest edition and other marine books (including tropical) at:

Hounslow & District Aquarists Society

Nick Dakin's Book Review Page

Advanced:

References:

Marine Aquarium Keeping by Stephen Spotte
2nd edition [John Wiley 1993]
ISBN 0-471-59489 -X

The Manual of Fish Health
by Dr Chris Andrews, Arian Exell and Dr Neville Carrington [Salamander 1988].
ISBN 0 86101 368 9.

Captive Seawater Fishes Science & Technology
by Stephen Spotte [Wiley Interscience 1992].
ISBN 0 471 54554 6. (reviewed at 03.01.34).

Aquarium Systems by Dr A Hawkins [Academic Press].

Academic Press   Second Edition   1998
ISBN   0-12-043792-9

1ST EDITION:  ISBN 0 -12-043790-2