Hi friends, here is very interesting site with:

A small collection of electronic circuits for the hobbyist or student.
Site includes over 100 circuit diagrams, links to related sites,
commercial kits and projects, newsgroups and educational areas.
Most of the circuits can be built with common components available
from Radio Shack or salvaged from scrap electronic equipment.
Most all of the circuits have been built and tested and believed to
perform as described, however possible mistakes may be found.