Defragger (could be part of OS)
CPU Cycles Donator
Any Graphic Adventure Game
Looking for specifics? That could easily get daunting, as each category has SEVERAL capable options. Mine are:
Windows XP Pro
ZoneAlarm (router for hardware)
Spybot and Adaware
Folding At Home
and of course there's various other user specific essentials (and non-essentials) on my system, such as CuteFTP Pro, Photoshop, Sandra, Nero, Roxio, Crazy Browser, Scanner Software, Ghost, and the list goes on.
I'm curious to know how you got Monkey Island running on a WinXP machine? Would that be the 256 Color floppy disk version, or the rereleased CD version?