David Odden's INTRODUCING PHONOLOGY (Cambridge University Press, 2005) is a textbook designed for undergraduates with just a basic linguistics course behind them. After the elementary matters of phonemes and allophones, Odden covers the rigours fo feature theory, phonological typology and naturalness. The final chapter on nonlinear representations makes a case for reconceptualizing data instead of ignoring troublesome facts, thus furthering theory.
Though I haven't made an exhaustive survey, Odden's is the best basic textbook of phonology that I have come across. It certain proves friendlier than the entry in the Cambridge Textbooks of Linguistics (red cover) line. He certain seems determined to turn out competent linguists of the future, as he goes through the steps of doing an analysis over and over again.
Odden is an Africanist, and the wealth of little-known African languages he has assembled here for example makes this an especially intriguing textbook. However, he also teaches basic principles through English, Russian, Finnish, and many more European languages. The wide-ranging and very challenging exercises further make this an excellent textbook. I've been in linguistics for years now, but I still profit from Odden's book, as going over the exercises once in a while keeps my skills sharp. It merits a look from not just first-year undergraduates.
Odden's textbook doesn't go too deep into the theory debate. Optimality Theory is mentioned a few times but never much described. However, he does give some recommendations for further reading after each chapter, so the reader will be able to go on to more specific material.