The internet can be a valuable resource for language learners. Here are some sites worth a visit. All of these suggestions are ones that I use on a regular basis or recommend to parents.
For Older Students
Veinte Mundos is an online Spanish magazine filled with articles for the language learner. I have my more advanced students use it. You can see this post I wrote on what the sites provides. It also contains a free printable to use with your students.
Listening to radio stations online is great for older students. Here is one site with lists of radio stations. Here is a 4-minute news report (TV) from Spain. Please note that with anything on the web it is always a good idea to monitor what students are watching and listening to!!
Printable Spanish has worksheets many of which are free. There are even some games. You just need to use the search box to look up the topic you are teaching to see what is available.
For Younger Kids
The Story Place is for young children. Simple stories in Spanish they can listen to online.
If you are teaching your own children Spanish at home Spanish Playground has a plethora of resources and ideas! I have used the suggested poems, games, and book ideas from this site! Love it! It is one of my favorite places to get ideas for teaching younger kids.