Lonely Planet Maldives (current edition) — the standard practical guide. Good on resort coverage and logistics, thinner on cultural depth. Worth having for the island maps and resort listings.
Guide to Maldives by Royston Ellis and Gemunu Amarasinghe (ISBN 1564408183) — older but gives better historical and cultural background than most modern guides. Good complement to Lonely Planet if you want to understand the country rather than just navigate it.
Diveplanit's Maldives — if diving is the reason you're going, a dive-specific guide will serve you better than a general travel guide. Covers atoll-by-atoll conditions, best sites, and seasonal recommendations.
For background on the politics and future of the country, look for journalism on Maldivian democracy (the archipelago had its first multiparty election in 2008 and has had a turbulent political history since) and on climate change — the Maldives is one of the most acutely threatened countries in the world, and several former presidents have made it a cause.