I generally use my hands. Left thumb under shaft, four other fingers massaging my balls while my right hand strokes the shaft in either up and down motions or pressured circular motions with my index and middle finger of my right hand.

Also have used : DizzyPen, rounded end of coke bottle through pants (somehwhat in public), vibrating toothbrush ( JadeFire suggested it to me bein my g/f and all ), misc other vibrating things.