Here are some podcasts relating to science that may be of interest for use with middle school and high school students:
Quirks and Quarks – a science-related radio show produced by CBC Radio One in Canada
NOVA podcasts – several different podcasts from NOVA, the highest rated science series on television
Science Friday – the popular NPR science show
The Science Show – a Radio National show from Australia
NPL Celebrating Science Lectures – video podcasts of lectures from NPL, the UK’s National Physical Laboratory (a little higher level than the others)
Here is a site that has a directory of many museums that are podcasting. These include science museums. What a great way to supplement your virtual (or real) field trips.
For advanced high school students, there are also a number of universities that podcast their lectures, such as Berkeley.
Of course, as with all podcasts and other web materials, make sure to screen individual episodes for studen appropriateness.