We try utilizing some of these podcasts in my 2nd grade classroom. Some of them are used as a whole class, and then others are used on individual student laptops or iPods.
CNN Student News (http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=17...)
Available through the iTunes store or the CNN Student News website at www.cnnstudentnews.com. These podcasts are a great introduction to global affairs for students. The host does a great job of providing relevant and interesting information for students. The students in my class love learning about new regions of the globe, and although some of the content is a bit too advanced for 2nd graders, we pick and choose which topics to dive in further.
Sesame Street Podcast (http://itunes.apple.com/us/podcast/sesame-street-podcast/id264537349)
These podcasts are high-quality and not very long which makes them perfect for small groups of centers during literacy. They have a great connection with Science and/or Social Studies (with an emphasis on culture). The kids love them!
Mathematics at PVUSD (http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=43...)
Found this great series of math-themed podcasts from this Arizona school district. They did a great job of using application-type problems to help students discover more difficult concepts and really explore their learning.
They Might Be Giants: Friday Night Family Podcast (http://itunes.apple.com/us/podcast/they-might-be-giants-friday/id26...)
We have been using these podcasts for years. The content is funny but actually covers some really great second grade content (especially around Science and Technology). The kids love to watch these on their iPods at home, or possibly during reading groups.