Blogs: a blog is a "web log." Many of them are free.
Bookmarking Sites: these allow you to access your favorite bookmarks no matter which computer you are using; you can also share your bookmarks with others. Diigo and Delicious are super powerful sites.
Listservs: when you join a listserv, your email address is added to a group of other email addresses; everyone who posts to the list is asking about or commenting on a general topic of interest. (One listserv Valerie belongs to is ili-l which is the information literacy instruction listserv.)
Twitter
Follow the movers and shakers in your discipline. (Valerie follows people like Joyce Valenza, Buffy Hamilton, David Pogue, and many others.)
Webinars
Tons of free webinars are available. Most are recorded, so if you can't make it in real time, you can watch the webinar at a more convenient time.
Wikis