The Singapore City Guide is, without a doubt, the most comprehensive LP resource on S'pore. It includes a huge pullout map of Singapore, as well as the usual, more detailed maps that are included in text. We've used this guide exhaustively, and it's been a great resource for what to see and how to see it. It covers some obscure locations (like Haw Par Villa and Yeo Swee Huat) which aren't covered in other guides. However, although the guide does a fine job of getting from place to place on the MRT, if you plan to utilize the Singapore Bus System, I recommend getting the publication from SBS (it's called the Transitlink Guide, and you can get it at local bookstores like Kinokuniya or from the ticket offices at MRT stations). Lonely Planet's bus directions are often more complicated than they need to be. If you plan on spending a substantial amount of time in Singapore (especially if you're moving here), I strongly recommend the City Guide. Looking at it before you get here will get you excited to come, and it will help you plan your trip. Having it while you're here will help you get around, and will definitely brand you as a tourist!
We also got the Lonely Planet guide to Malaysia, Singapore, and Brunei The book is much bigger and covers much of the same information as the Singapore City Guide, but with less detail and fewer maps. Plus (obviously) it covers both peninsular Malaysia, Malaysian Borneo, and Brunei. This is pretty valuable, because most people don't just come to Singapore without visiting anywhere else. Malaysia is the most convenient place to visit from here, so it's nice to have some information about it. This guide also helps to create a bigger picture of Singapore- it's not just a modern island in the middle of nowhere. It's surrounded by Malaysia and Indonesia, which have some interesting similarities to Singapore, but with some obvious and sometimes startling differences. I recommend this guide if you're planning a medium-length trip that focuses on Malaysia and/or Singapore. If you'll be in the area for a few weeks, this should cover everything you need to know.
The last guide that we bought is Southeast Asia on a Shoestring This weighty tome covers eleven countries in this region (Brunei, Cambodia, East Timor, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand, and Vietnam). The book gives supreme budget travel advice, and is perfect for the recent college grad going on a "find-yourself" trip around SE Asia while trying to stretch that graduation money as far as possible. Obviously this book covers a lot more ground than the other two, so by necessity there is a lot less detail. We've really liked using this book for planning some of our shorter trips- like our long weekend in Kuala Lumpur. Because it has less detail, the things that it mentions are usually either the best or the most popular. However, because it focuses on doing everything the cheapest way possible, we sometimes refer to other sources for mid-range hotel options, which tend to be more our style. As a couple, it's better to have our own room with our own bathroom than it is to shack up in a hostel with a bunch of others. I recommend this book if you're a young person on a tight budget, or if you're planning a long, meandering trip through SE Asia. In fact, the beginning of the book makes several itinerary suggestions for trips lasting from one to six months.
Obviously I'm kind of a loyal Lonely Planet follower, so I don't have too many suggestions about other kinds of guidebooks. We did recently borrow our friend's Insight guide for Bali & Lombok to help plan our upcoming trip to Bali. It's been really helpful, and one thing that I prefer about Insight Guides over Lonely Planet is that the Insight ones are full of beautiful color photos. I'm kind of a visual person, so I like to ooh and ahh over the photos while planning a trip. Plus seeing photos of a place can really help me decide if it's the kind of place I'm interested in visiting. However, I still think Lonely Planet does a better job of providing details on things like specific locations, price estimates, and how to get places. I also prefer the layout of LP books, but that may be in part because I've been using them for a long time and have grown accustomed to them. Overall, I think Insight Guides do a great job of getting you pumped up about where you're going, but LP guides offer the practical advice that can help you make it a reality.
Although I don't have as much experience with the other types of guidebooks, I know that the Singapore Insight guide and the DK Eyewitness Singapore guide are especially good for people that are image-hungry and like to look at pretty pictures, but I think that DK caters to a lot of the most popular, touristy destinations (which might be fine for a shorter trip). The Singapore Rough Guide is another that I see tucked under the arms of foreigners wandering the city. This guide looks a lot like the LP Singapore City guide- mostly good if you're planning a longer trip here and need a lot of information. There are loads more, like Fodor's Singapore, plus a bunch of small pocket guides and top ten lists, like Frommer's Singapore Day by Day, Eyewitness's Top 10 Singapore, and the Berlitz pocket guide, which looks convenient for being a little more discreet about your status as a tourist.
We did purchase one other Singapore book before leaving the U.S. A friend recommended the Culture Shock series, which he said can be especially valuable for people planning a move abroad. So we purchased Culture Shock Singapore. It's an interesting resource on how to conduct yourself in Singapore without horribly offending anyone. I find it interesting, but I think it was difficult for the author to give good advice for Singapore, because so many different races live here. Advice on how to behave if you're invited to a Chinese family's house might not apply if you're invited to an Indian family's home. Also, pretty much everyone here seems aware that they're living in a modern melting pot of a city, and I think that for the most part, people are pretty forgiving of the social faux pas of foreigners. The most general advice usually serves me well here- just watch what everyone else is doing, and try to match that pretty closely. And be nice. I do think that the Culture Shock guide makes for interesting reading, and gives a little insight into the background of the average Singaporean. Although it didn't seem strictly necessary for Singapore, I highly recommend Culture Shock books for people going to more culturally sensitive countries like Saudi Arabia.