I ran across this article on Digg today. It's PC World's opinion of the 25 Greatest PCs of all time.
The article is located here.
Several systems don't qualify as "retro" by any means. Second Gen iMacs were introduced in '02. Most of them, however, are either retro or just plain old-school. Some of the systems on their list are older than *I* am! I'm somewhat disappointed that the sub-$100 Timex Sinclair 1000 (my first computer) wasn't on the list, seeing how it was the first really affordable home computer. On the flip side, it was kind of difficult to use, but not much worse than the Tandy TRS-80 which didn't sell nearly as well.
The HP100LX, a dos-powered precursor to the HP300 series I wrote about last week made the list, and several other systems that were ahead of their time did as well. I won't spoil too much for you, though. You really should check out the list. It's a good read but with a few paragraphs for each item on their list, you should prepare for a bit of a read, or bookmark it for later.