Many reuses: Do not forget  http://www.instructables.com/id/Reuses-for-legacy-computers-II/


Turn your old equipment into musical instruments: https://www.youtube.com/watch?v=dmoDLyiQYKw
Who said that old computer could not do graphics or show movies: http://www.instructables.com/id/Graphics-in-a-text-world/
Funky Clock http://www.instructables.com/id/Old-laptop-or-pc-into-a-clock/
Cdrom motors for mini-robot.
Security system
Old Apple imac 192 meg ram into linux deskop. (something I did a while back)
(Operating systems that support really old computers. openbsd, deli linux, and etc) (Most linux distros (but not all) will support PII or better. Debian, Ubuntu, and etc will.
support most "New age" ppc macs.)
Old computer as a server. (web email, music, file, print, router, and etc.) (www.howtoforge.com and there are a ton of instructables)
Security system http://www.instructables.com/id/Security-with-a-old-Pentium-1-Part-II/
Turn a pc into a sort of diskless thin client. http://www.instructables.com/id/PC-personal-computer-into-a-sort-of-thin-client/
Monitor as a tv. http://www.instructables.com/id/Setting-up-a-computer-based-DVR-with-Mythtv-for-l/
Parts for other projects. http://www.instructables.com/id/Computer-controlled-OTA-TV-antenna/
Clothing accessories. http://www.instructables.com/id/Techie-bolo/ http://www.instructables.com/id/Cat5-belt/
Pet cage from an old monitor. (Be sure to check for any health risks)
Computer case shelf.
Toilet paper dispenser.
Barbecue pit.
Computer controlled coffee maker.
Digital frame.(lots of instructables on this site.) http://tinyurl.com/4pejnyu
Computer case coin bank.
Art pieces
Bread bin. (Be sure to check for any health risks)
Furniture
Computer desk support from old cases. (be sure to secure well) (one case high and you have a coffee table.)
Knife sharpener (or computerized lazy Susan?)
Wall paper
Coasters
Archway
Science data collection workstation (also teach science)
Baby rocker ((eject; eject -t) script loop in linux)
Home automation. http://www.instructables.com/id/Linux-beginning-home-automation-on-a-server/
http://www.instructables.com/id/Home-Automation-MSWindows-XP/
Teleprompter. http://www.instructables.com/id/Linux-ghetto-Tele-prompter/
Soldering hand. (just an old at power suppy case side with some coat hangers and clips)
Set up you own private intranet to hone your networking skills. (i.e. how dns works)
Make someone happy. (www.freecycle.org )
Check this out too: http://www.instructables.com/id/Computer-Recycling-and-Repurposing/ .