The website Lernu.net is one of the best Internet resources an Esperantist can use. They have all sorts of exercises and learning materials for all different skill levels. My personal favorite tool from the good people at Lernu is their Word of the Day feature. Every day, they put up a new Esperanto word, and give full, dictionary-quality definitions and sample sentences. Give it a look, or bookmark it - the site gives you a bite-sized fact to learn while you wait for your email to load, or something similar.

There is also a way to subscribe to Lernu’s Word of the Day service via email, but it requires that you register for a Lernu profile. It’s free, though, and a profile also lets you track your scores.