Editor's Note:I haven't built any of these yet, but I've sure heard good things about them.
The hobby of building one's own electronics is certainly a dwindling one. All the same, electronics is a field that just keeps getting better. Particularly, audio electronics. Their one field that can still be built by hand. Infact, some of the coolest low-distortion gear can be made by hand.
I found a wonderful resource of really cool, audiophile quality projects for just about any application. Check out: http://sound.westhost.com/projects.htm