Well this is what worked for us (although it only worked after she mentioned interest...previous attempts to potty-train her did not work until she brought it up herself). We used a sticker reward chart.
We went to Michael's with her and she helped pick out several packs of small stickers that she liked (most featured Disney shows and cartoons that she was really into at the time). We also picked out a couple packs that had REALLY large stickers, featuring characters from the Toy Story movies (she was VERY into those movies at that time). I also got a sheet of foam poster board, which I divided into 3 sections: one section was for tee-tee, one was for poo-poo, and one section was for accident-free days. Every time she went tee-tee in the potty, she got to pick one small sticker and put it in the 'tee-tee' section of the poster. When she went poo-poo, she got to pick TWO small stickers and put them in that section of the poster. So, that helped a LOT with giving her incentive to go potty in the toilet.
But, we still needed something to give her incentive to ONLY go potty in the toilet (in other words, she would go potty in the toilet so that she would get stickers, but then she also continued to have accidents in her panties as well). So, if she went a whole day without having any accidents in her panties, then we let her pick out a BIG Toy Story sticker to put on the poster at the end of the day. Once she had 5 big stickers, she got Woody and Buzz Lightyear dolls. It worked awesome. FYI - she was 32 months old at the time; I only think that particular system worked because she was so obsessed with the Toy Story movies.
The other thing that helped was getting rid of the pull-ups. When we first started the reward chart, we kept her in pull-ups, and she just kept peeing in them. Switching completely to panties, even though it meant dealing with accidents from time to time, helped greatly in keeping her from going outside of the potty.