17" 1.25 GHz G4 iMac. Coming up on 3 years old now, and still running as great as the day I bought her. Although I'd like a new Mac, it's tough to justify buying one when my curerent one is still working perfectly fine and meeting all my needs!
I'll probably upgrade in 2007 or 2008 once a 20" Conroe iMac with 500 GB HDD and 4 GB RAM options, HD-DVD/Blu Ray optical drive, 802.11n and Leopard pre-installed is available. Or a Conroe min-tower of some sort...
Mac Mini G4 1.42 (unjustly slighted in this poll by not being dignified with an entry of its own)
A fine machine in its own right, it served as a testbed to see if moving away from the train-wreck-previously-known-at-longhorn was viable. Now to be retired (my mother wants it) having demostrated decisivly that it is. To be replaced by a soon-to-arrive-honest-it-will-just-be-another-two weeks Mac Pro.