G4 Powerbook 1.67 GHz "The Last One" (of the G4s)
Titanium Powerbook G4
Powerbook G3 "Wallstreet"
Power Mac G4 dp
Power Mac Beige G3
Power Mac 9600
SuperMac Mac clone
...and a few more.
They rarely die as they age, so I just use them for less mission critical work, and as loaners.
You won't believe the number of PC users I've converted just by loaning them a 2 year old Mac! heh heh
I have a recording studio, so I use the older machines as dedicated CD burners, Label Designers, eMail, calendars, etc.
I am planning on getting a Sensus Ultra from Reefnet, because it works with Macs. Palm OS too. It is not a dive computer, but simply records the data (depth, time, temperature, etc.) for download later. I have not used one yet, but I hear good things, and they record your dive profile in greater detail than most dive computers. They are not as expensive as a computer and are very small and easy to clip onto your BC.
I am in no way associated with ReefNet or their products. It's just a cool device that may be a solution for some of us.
http://reefnet.ca/products/sensus/
The guy who does the Mac downloader/Log for Suuntos
http://www.macdivelog.com/, says he is working on support for Oceanic, so I am happy about that!
There is a nice looking dive planner that is written in Java that will run on Macs.
It is at:
http://www.wittig.net.au/diving/mvplan.html