I disagree with those who said Madhur Jaffrey's Indian Cooking was simpler--I found this one easier to follow and the recipes less complicated, yet equally as delicious. For the beginner, Sahni also takes time to explain basic techniques, concepts, and spices which are necessary to Indian cooking but may be unfamiliar to Westerners. She even explains how to make chenna and paneer (and then how to turn it into ras malai, which I recommend highly).
The recipes included are wide-ranging (definitely more in here than Jaffrey's) and an excellent introduction to Indian cooking. It's the best basic book on the subject I've used.