Here are some links for some PIC based o-scopes. I plan on building one here soon.
http://www.semifluid.com/?p=29 lots of good oscopes Easiest
http://www.serasidis.gr/circuits/AVR...cilloscope.htm AVR oscope
http://www.instructables.com/id/Buil...rum-Analyzer-/ dsPIC oscope, looks about the best
Non pic based ones