Today by, way of your screenshot, I discover Asm-Pro. Just got into Amiga recently (by way of receiving one from my uncle's closet..) and have been meaning to backfill my shameful lack of 68k asm knowledge. Thanks!
For a quick test/code loop nothing beats the Asm-* family - remember to save often and make backups though :)
Another modern/maintained one, focusing on low end 68000/68010 machines, is asmtwo.
AsmOne was a very popular assembler at the time, and has seen a few derivatives. I remember an old one called trash'm'one.