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

http://members.chello.nl/r.dekker49/.../uscope_e.html

http://www.dansworkshop.com/Homebuil...lloscope.shtml