1. Check out Neil deGrasse Tyson, who hosts the excellent show Nova ScienceNOW, currently in it's third season. It runs just after NOVA for several weeks in a row.
2. Try Robert Krulwich, who co-hosts the great NPR show & podcast RadioLab, with the equally wonderful Jad Abumrad. They are great for driving and listening.
Both are brilliant at making complicated sciencey topics seem fun and interesting. My 13 year old daughter enjoys both shows immensely with me. RadioLab, especially, is fun and funny, and you can gather up all podcasts on iTunes (there are about 25 full shows presently, plus lots of smaller in-between podcasts).
Both of these guys appear frequently on public radio shows too, like Ira Flatow's Science Friday, which is also good but a little more current eventsy.
Hope you enjoy these!