Gah...can`t settle on one since the two I thought of both have sentimental value as well.
A basic dildo my first female master(really,my first REAL master)got for,and used on,me.The helplessness of being fucked by a woman weaker than you...*shiver*.
And then there`s a paddle I got at an anime convention.
Black leather on one side,silver studs around the sides,lace and ribbon on the front.Oh,and studs forming a pretty cross.It became infamous around the con by about fifth time someone took it and ordered me to bend over.