One of the podcasts I listen to on the way to and from work is, "A Way With Words" - it's fun to listen (yeah, that's right, a show about English is fun to listen to) and I think listening to it got me about 20 points on the GRE (when I was preparing to take it, I had been listening to AWWW for about 2 months.)

One thing that I've always thought was really odd was the large percentage (I'd say 50%) of their call in listeners from Wisconsin. Some callers are kind of over the top with their criticism of other's grammar, but the Wisconsin folk usually have really interesting questions that they've been thinking about for a long, long time.

AWWW is a fun show and you should check it out if you've got the time. I learn at least 5 things every time I listen.