In order to identify species there is, in my personal opinion, nothing better than a personal library of books! This can be a considerably expensive exercise if you adopt a comprehensive approach, as I have found to my cost (literally!). I have a library of approximately 400 books on natural history and, apart from taking up ever increasing storage space, only ever seems to highlight the areas I haven't got covered, resulting in yet more purchases. Increasingly, I find myself turning to the 'Interweb' in order to confirm an i.d. or at least to give me an indication of where to focus my further investigations. However, be warned! There is an awful lot of mis-information out there. Don't trust everything you read and, if possible, cross check against as many different sites as you can find to verify the accuracy of your data! When buying books, don't always presume that Amazon is the cheapest! I've often found titles for sale by independant retailers at 10% of the cost offered bt Amazon. Do an Internet search based on the full title of the book you require, maybe also with the Author(s) or the ISBN, if you know it. I've found books at £30.00 that would cost me £300.00 on Amazon!
A list of my favourite sites, all dedicated to some form of natural history.
CalPhotos. A database containing in excess of 400,000 (increasing by 800 per month) images of animals, plants, fungi, landscapes, and people and cultures, searchable by almost any criteria you can think of.
Ecology Asia. An excellent site providing information about the wildlife of South East Asia, with an emphasis on Singapore.
World Bird Guide. Just that! A photographic guide to most of the bird species on the planet.
BugGuide.net. Does what it says on the can, but only for the North American continent. If you've a photo of an unknown insect taken in the USA or Canada, here's the place to get it identified!