Like Lillian, my all time favourite book is Ann Ladbury's Sewing but I do have other favourites too. I agree with Utta about Alison Smith's books and you can often find these in The Works at very good reductions so well worth checking there if you're on a budget.
A small pick of my other favourites would include:
Claire Schaeffer's Fabric Sewing Guide, not only to help with identification but lots of useful information on best uses, construction advice/techniques and practical sewing settings (most appropriate needles, threads etc.)
Lynda Maynard's The Dressmaker's Handbook of Couture Sewing Techniques which has so many examples that can be incorporated into everyday sewing projects.
Time Life's The Art of Sewing/ The Professional Look It's part of a series and a good set to look for in second hand book shelves. It's very much diagram based but very understandable for that too.
Julie Cole's Patternmaking with Stretch Knit Fabrics is one of very few I've found for knit fabrics but has proven to be just what I needed. It gives three different versions of each block for low, medium and high stretch which is perfect for me as I wanted them for casual knits for me and my DD but also for tight-fit lycra dance costumes too and there's a big difference between the two! Expensive certainly but it's opened up a world of opportunities.
I'm attaching pictures as, if you're anything like me, you'll recognise the cover more easily than the title or author.