#17 and #18 - I very much like Simple Chess and Chess Structures.
IMO Silman's Endgame Course is best if you're starting from more-or-less nothing - if you don't know how to play king and pawn vs king, for instance, or king and piece versus king and pawn. If you're starting from a higher baseline then it might be worth getting something different.
I do agree with
@tpr on properly going through what you've already got before buying more books, though.