The following are some free "feed reader" or "news aggregator" programs, which get updates from websites through "RSS" (rich site summary). This lets you find out about new pages on websites without having to go to each individual site. For a bigger list see Wikipedia.
Note: Safari seems to have built-in RSS support.
These are all extensions to the open source, multi-platform Firefox web browser:
Note also that Firefox has built-in RSS support through its Live Bookmarks feature.