I agree that children do it when they're ready. Unfortunately for me, I was in the same boat as you last summer. I needed my daughter to be potty-trained by the end of August. I started the last week of July and went a tad bit insane. Here are some of the things I tried:
Change rewards often! Our treat system: one treat for sitting on the potty & trying and two treats for results. She didn't like sweets, so I offered peanuts, cashews, chips, sweet tarts, etc. She only got this type of food when potty-training. When she lost interest in the reward, usually within a day or two, I brought home something new. That worked for a while.
We also tried the naked technique. My girls LOVE to run around the house naked. One day I noticed that when she didn't wear any clothes, she rarely had accidents. Wonderful news... but only if she could go to school naked!
My ped. told me that my child knew what I wanted and that I should simply stop talking to her about it. So, instead of reminding her to sit on the potty, like most 2-3 yr olds she didn't care to be told when to go, I would simply sit down with her "treats" and pretend to eat them, proclaiming how wonderful they tasted. Most every time I did this, she would immediately run to the potty to try.
Also, my ped. said once they're out of diapers/pull ups, not to go back. We also tried training pants for a while in lieu of regular undies. They are thicker and more absorbent than undies and the child can feel the wetness immediately.
In the end she was potty-trained in time to start school and I regained my sanity. Well, most of it! Good luck.