My favorite Macs, by far, are the old original all-in-one 68k Macs with the little 9" screens. I first used a Mac SE for music theory homework while taking classes at GCC in 1989 or 1990.
I love MacQuariums. But don't ever let me hear that you've done this to a working Mac! There are plenty of old non-working classics around for making an aquarium.
Old compact Macs can still do cool things, and even browse the web and get email. One of my old SE/30 machines has a 10-Base-T ethernet card in it, and can also act as a low traffic web server.
There's to much to fit on this page on the Macintosh and it's development.. But here are a few links to some sites with lots of cool history and info on the early Mac computers.
Folklore.org (by Andy Hertzfeld) Anecdotes about the development of Apple's original Macintosh computer, and the people who created it.