I think Google Reader is the easiest and most accessible tool. Works well with Android Phones & iphones as well.
Heck, itunes is an aggregator as well. I suspect that you are talking about blogs & forum entries.
See the RSS link at the bottom of this page? You can use it with a reader to collect all the stuff people add to this forum.
I highly recommend google reader- it let's you organize all your online reading (blogs, wikis, newspapers, anything with an rss feed) Google reader also allows you to share any entry you find informative with anyone on your gmail address book which is great to share with teaching partners or others in your school. I've actually been showing my 6th graders how it works and am pushing it with a number of them who are quite technologically literate.