In order from the most used to the least:
Greenlee BEHA Unitest
Etcon polarity / GFI test
Ideal Pathfinder for USOC, CATx & coax (with toner)
Generic VOM ~$12, less if I find one
Non-contact volt sniffer
Amprobe clampon
Generic buttset
Ideal ABS (Almost a Buttset)
Amprobe open finder