VDosplus - a great DOS emulator for Windows derived from DOSbox but
for non-gaming applications.  The IBM Macro Assembler version 2,
Debug and exe2bin from PC_DOS version 2 all work fine in it and these
are the programs that Robert Lafore is using in his book "Assembly Language
Primer For The IBM PC and XT".  
AppleWin is an Apple2 emulator for Windows and loads The Visible Computer
disk image which goes with the book "The Visible Computer 6502" - this is
a fun teaching tool for assembly language.
The two emulators I forgot to put in a torrent I just uploaded - 
"Assembly Language Learning Tools" so I'm uploading these folders 
separately.  It always happens! - I forget something