Two of my favourite cook books of all time "Enchanted Evenings" and "Special Occasions" by John Hadamuscin
I love the way these book are laid out by seasons and events, with beautiful photographs. I have adopted many ideas and borrowed parts of his recipes. He has included many recipes by his relatives and shares my passion for getting back to our roots and keeping alive the food of our ancestors. I have had these books for about 20 years and still refer to them often.
Another book that I refer to all the time is "the essential Mediterranean Cookbook"
This is a book that I bought about 8 years ago from a school, where it was left along with several other books for any of the staff to buy, I could not resist the pictures. Any way I still look at the pictures and use it often for ideas and inspirations.
The best book I have ever found for baking is "in the sweet kitchen" by Regan Daley
As the subtitle suggests this is the definitive Bakers Companion. The first half of the book is more a text book about baking than a recipe book with substitution suggestions and an exhaustive list of baking ingredients with information. The second part is recipes and everything I have ever made has worked beautifully. My parents bought me this book for Christmas one year after hearing the a glowing review on the CBC. I am very grateful that they did.
Two more books that are go to books for ideas "Summer" and "Winter" by Delia Smith. Delia is kind of the English version of Martha Stewart, though I find her recipes way more reliable.
For indian recipes that are easy to follow and always work it is hard to beat Madhur Jaffrey another English Icon.