I have only done 1 podcast with my class, it was very easy to do. I followed the directions I found on-line here: http://www.how-to-podcast-tutorial.com/index.htm
I liked this site because it walks you through everything and shows you what your computer screen will look like. It also has all the links you will need for downloading the free software you will need.
As far as what to podcast you can do it on pretty much everything. We were doing a How to Unit so we recorded one of our shared writings of how to. You could use this as one of your final publications. Once they have finished up a unit you could have each of them record their final draft. You could also use it with your RW having the students podcast anchor charts (if you are doing reviewing right after the break). You could have guided reading groups or lit groups discuss books. If you are starting a new math unit you might want to have them podcast how to do ____ (measuring for example). Have your class discuss science or social studies units.
Really the list could go on and on you just need to decide what areas you want to start with - maybe areas that have gotten a little stale to get you and the kids interested again. Have fun and good luck!