I've sung the praises of Averbakh's Chess Endings: Essential Knowledge more than a few times on Chess Tales, but have been reprimanded by one reader for not mentioning Karsten Muller's Fundamental Chess Endings.
The subtitle includes the word 'Encyclopedia' which usually makes me wary, but I have to say the reviews are outstanding and the blurb sounds enticing: firstly it's accessible to beginners (and experts!), providing tuition, principles, and practical play guides as well as reference, and secondly, it benefits from computer endgame tables and analysis to ensure the variations are sound.
Let me know your thoughts if you have a copy. Thanks!