Assuming you are interested in learning not just Assembly but how to use it in conjunction with a high-level language (almost always C/C++);

Background:

--- Matt Pietrek's "Just Enough Assembly Language to Get By" - http://bytepointer.com/resources/pietrek_asm_pt1.htm

--- Hongjiu Lu "ELF: From The Programmer's Perspective" - http://beefchunk.com/documentation/sys-programming/binary_fo...

Books:

--- Computer Systems: A Programmer's Perspective (3rd Edition) by Bryant & O'Hallaron - https://www.amazon.com/Computer-Systems-Programmers-Perspect...

--- Modern X86 Assembly Language Programming by Daniel Kusswurm - https://www.amazon.com/Modern-X86-Assembly-Language-Programm...

--- Low-Level Programming by Igor Zhirkov - https://www.amazon.com/Low-Level-Programming-Assembly-Execut...