Get yourself over to the weight lifting thread and pay attention to what those ladies say, cause they're genius! Basically anything Mel or Meg says is gospel.
Since adding weight lifting to my routine, I've lost from a size 18/20 to a size 8/10, and that's been since October 2009. In four months.
Really.
And I've made this progress by cutting back on my cardio time, and adding strength training. Instead of walking the 60-90 minutes that I'd been doing for 2 years, I started running. I started out running 60 seconds, the walking 2 minutes, for 30 minutes. Every week I increased my running time, decreased my walking time, until I can run 3 miles in 34 minutes. If you don't want to run, you can achieve the same thing but using inclines on a treadmill.
As for the strength training, you should check out a book called Body for Life, by Bill Phillips. There are other books/programs out there, of course, but I've been following this program and can testify that the results are dramatic. I'm on week 6, and yesterday I walked around my office demanding that my co-workers check out my biceps.

For the first time in my life, I actually have definition, instead of squishy arms. I think part of the reason I'm succeeding this time is that I've given up the girly weights. Before starting this I couldn't lift my 5 pound dumbbells easily. I just bought new weights yesterday that are 15lbs each, and have no problem lifting them over my head for 12 reps. Sorry about the novel length post, but the progress I'm making has me trying to convert everyone.