Michael - A very simple Cmaj7 fingered 032000 is the one usually used in Celtic music. It keeps all the notes of the Em except that it changes the B note on the 5th string to a C. The B note on the open 2nd string is still there.

CAUTION: Use this chord sparingly! Occasional use will make people go, "Wow! Cool!". Excessive use will make people wish you would go play somewhere else.

Bruce