Always forgive your enemies - nothing annoys them so much. 

Forgive your enemies, but never forget their names.

It takes a strong person to say sorry, and an ever stronger person to forgive.

The things two people do to each other they remember. If they stay together, it's not because they forget; it's because they forgive.

The stupid neither forgive nor forget; the naïve forgive and forget; the wise forgive but do not forget.

 
http://www.boardofwisdom.com/default.asp?topic=1005&listname=forgiveness