I used the technique described in the book "Potty Training in Less than a Day". Here is my experience- for my very stubborn, high-intensity, ADHD son it seemed unsuccessful at first (this technique involves a very intense 4 hour training session.) Within 2 hours I gave up and put him back in Pull-Ups (this was at age 3.) One month later he came to me and said he was ready to wear underwear and get rewards! And he did not have any accidents at all- he remembered everything from the training session and even told me what he was doing (words straight from my mouth from the session.) So, while it was not "in less than a day", it was successful once he decided he was willing to do it. He still wore a pull-up at night though.
When my daughter was three I tried it again. Things went much better for her, but it was still more like 3 days before she was completely trained (just a few accidents in those 3 days.) She also still wore a pull-up at night.
I plan to do it again when the time comes for my 3 month old! I like it because you are actually "training" the child to recognize when they have to go to the bathroom, not just saying "OK, tell mommy when you have to go pee." This technique was developed in the early 70's originally for mentally handicaped adults who were not yet potty trained- but they adjusted it for children and found that it worked very well.
If you are opposed to giving your child food rewards then this technique would not be for you. My kids both asked for the rewards for a few days after the session- I told them that they would get the reward only after dinner if they kept their pants dry all day and then only for one week. They were fine with that and did not even remember to ask for the rewards after about 5 or 6 days.
Hope this helps! Good luck with whatever you choose to do. I liked this one because it was not a long, drawn-out process- six months of taking them to the bathroom every hour or so was not my idea of fun! My biggest piece of advice is DO NOT use the disposable potty training pants!!! They are just fancy diapers and the kids know it! Buy the cloth training pants and just be prepared to wash them!
P.