At present my main computer is a 21.5 inch iMac around 12TB of external storage, use it as a server and for everything else in the house. It replaced my first Mac (white intel iMac) which i sold to my family after i fixed a hard drive failure.
My girlfriend also got me a 15inch iMac G4 a few years ago which runs Leopard. Intended for it to be a server but ended up being a funky looking kitchen hifi and print server. Gets loads of attention when we have guests.
She got me a special edition ibook clamshell a few weeks back in perfect condition (a 466Mhz Graphite with half a gig of RAM and a DVD ROM) which is my new pet project. currently trying to make it as useful as possible. So far ive got it doing the following:
- Its runs the latest release of Tiger (with spotlight, dashboard and a few graphical options disabled to give it a performance boost)
- Camino for light web browsing
- Dropbox syncing
- scheduled backups of the system onto a tiny USB memory stick which doesnt stick out of the case

- Mobileme syncing for iCal, Mail, keychain
- iTunes 8 - for playing the shared iTunes library on my main iMac
- Access to bunch of media/document network shares on my iMac
- Printing over the network to my iMac G4
- A battery health monitor (displays number of charge cycles and other battery health things)
Im still trying to find a good lightweight word processor to use on it. I have installed Bean but havent really tried it yet.
I also have a slot loading imac G3 lying around which makes a very high pitched buzz most people cant hear, but i cant find a use for it so never tried to fix it or use it