Two quick things... BabiesRUs has these things that you put into the toilet bowl. A cheaper method would be to throw in cheerios. Either way, tell him to aim at them or try to sink th O's. I know it sounds silly, but it works.
Try getting him to sit backwards on the potty with a book or toy on the back of the toilet and whenever he does go in the potty give him a reward i used tootsie rolls (from halloween) but only when he reminded me. Also maybe a friend of his is potty trained tell him that his friend goes in the potty like a big boy... Positive influence!!!!!
after two years of trying i finally started going "come on baby lets change that diaper." he'd go "i'm not a baby." and i'd go "you must be. babies wear diapers. big boys use potties." so he started going to prove he was a big boy. cool undies help too. i got him some and told him "don't pee on the red power ranger now, okay?" good luck.