Without a doubt, my Amiga 3000 TUX machine. When I was at Purdue University, that machine was the bomb. The professors I had couldn't believe that I could 'dual-boot' between UNIX (SVR4 no less!) and the AmigaOS. I even had the 2410 Graphics Card for sweet, sweet, X-Windows goodness.
The deal was much better than the overly priced NeXT Cube's that Steve was pushing to college students back then.
Later, I added an Emplant board for Mac emulator. Boy, those were the days.
Now, I'm the professor and my students are just amazed that I didn't own a Windows machine. Commdodore? Atari? NeXT? What are those??
I guess you really can't go home again.
-Pen