D.P.
I second the patience answer. There's nothing worse than a power-tripping two year old when you've lost patience. A couple of good potty books are worthwhile too. I made a cool chart with some color printouts of his favorite characters and used stickers for rewards -- all was great and I couldn't believe how easy it was until after another week or so, it all went down hill. Good luck -- most useful too would be a support group. I did not have that and wish that I did. GOOD LUCK!