M., I think that few things are as frustrating as potty training! Don't you just wish you could push a button and make them do it? With our 3rd child, nothing worked! He was 2 1/2, but I'd tried everything you have, too, and those things had worked with two other kids, so what was the deal now? Finally, we simply told our child that I would no longer be buying diapers and he would have to be a big boy and learn to go on the potty otherwise he wouldn't be able to go do all the fun stuff we get to do outside the home since his clothes would be wet. It was a tough week, and sometimes I felt like I was taking steps backwards instead of forward. But after about 3 days of sticking with it, he was trained. Day and night trained! He still has the occasional accident at nighttime, but I think when he realized he had no choice but to do it, he decided it was more important to choose to go on the potty than miss out on the fun (going ot the zoo, to the park to play, to swim at the neighbors house, etc.)
One more thing -- I know lots of moms are advocates of pull=ups, but I have found that they simply hindered our training efforts. <y kids would use the pull-ups as a "crutch" -- they weren't something special. They were just still a diaper to them. So I will not use them with my 4th child for that reason.
Good luck and hang in there!