Mightymon 128 v4.00.10 by Bruce Craig (Released August 1st, 1990) with contributions by Kevin Phillips and Andrew J. Galluchon.  This is one of the finest machine language monitors you'll find for the Commodore 128.  Documentation is included in the archive.

Move 80f by Donald E. Bradley is a cool little Commodore 128 utility that found it's way onto Qlink back in the day.  With this utility, a Commodore 64 program running on a Commodore 128 (in c64 mode) can access the 64k VDC memory to store data.  Full docs are included in the archive.