Here's my list of great cookbooks I still own (culled from almost five linear metres at its peak), in alphabetical order by first author, with commentary. Many of these should be available at your local public library. Some of the other books I still have are good but not great and hence are not on this list, mostly on Asian cuisines.

Rick Bayless and Deanna Groen Bayless: Authentic Mexican
Bayless is a celebrity chef now, but he wasn't when he wrote this book; at that point, the Baylesses only owned and ran an excellent restaurant in Chicago, Frontera Grill (which stil exists, though my last meal there was less than satisfactory). This book isn't entirely authentic: there are some Bayless creations that marry traditional methods with a nouvelle sensibility. But it is all done in a spirit of respect and love, and with detailed, precise directions. Real Mexican food is fabulous in a way that Taco Bell and store-bought bottled salsa can only hint at, and it is so rare in Canada that you really must cook your own. His followup book, "Rick Bayless's Mexican Kitchen", is a good source of what one might call fusion ideas, as well as some more authentic recipes. More recent books are not up to scratch.
Carol Field: The Italian Baker
"The Italian Baker" is a detailed look at breads, rolls, pizza and foccacia, cakes, and cookies from many regions of Italy. Field has travelled in Italy cadging recipes from master bakers, successfully adapting them to the home kitchen.
Marcella Hazan: Essentials of Classic Italian Cooking
This book is a combination and augmentation of her quintessential texts, "Classic Italian Cooking" and "More Classic Italian Cooking". She has lost some of her fussiness (she no longer advises one to peel chickpeas for soup, or rants about what some people put into lasagna) and the recipes are lower in fat and sugar. Solid and comprehensive.
Maida Heatter: New Book of Great Desserts
Maida's books make the best desserts I know of: they nearly always work no matter how intricate they are, and she is constantly reassuring you and telling you what things should look like, or to continue at this point or that despite the appearance of failure. At one point I had a reputation for dessert-making that was due entirely to her. I also have "Great American Desserts", which is as well-written but not as interesting, and "Great Chocolate Desserts", which is more specialized, but still of high quality.
Julie Sahni: Classic Indian Vegetarian and Grain Cooking
Whenever friends ask for a vegetarian cookbook, I recommend this one. Sahni's books do justice to the incredible diversity of Indian cuisine and to the range of legumes, nuts, seeds, spices, and vegetables used. Her instructions are clear and the recipes work wonderfully. Her "Classic Indian Cooking" covers the sort of food found in North American Indian restaurants, while "Moghul Microwave" shows how to take advantage of new technology. Avoid her recent book, which oversimplifies the cuisine for lazy people.
Lorna Sass: Cooking Under Pressure
The first pressure-cooker cookbook I know of to take the appliance out of the '50's. Risotto in six minutes of pressure, no stirring, with a texture that is almost indistinguishable from the real thing (which requires twenty-five minutes of continual stirring). Chicken and lentils in twelve minutes of pressure, stews in half an hour. This book lets me leave work at half-past-four and have a meal good enough for company on the table at six. The followup "Classic Vegetarian Cooking Under Pressure" suffers from not enough familiarity (or engagement) with the truly great vegetarian cuisines of the world, but there are some nice recipes in "The Pressured Cook", though the spicing is suspect. Take these as starting points for your explorations.