Coolmath4kids has a number of resources and activities for students, parents, and teachers. I would recommend saving this for a resource that you can add on your future classroom website. There are multitude of games for your students as well as 'lessons' that kids and parents can use to work on math together at home!
This site offers an array of resources related to teaching mathematics. It includes links for teachers, students, and parents. While some of the information needs to be purchased, there are also free links. For instance, the website offers flashcards to use to assist students. The website also contains games, such as crosswords, to help familiarize students with key vocabulary.
This website is a great resource for brain teasers, questions of the day, or trivia related to mathematics. This can be a great resource for teachers to find a "hook" to begin their math lessons. This site also contains many outside links to additional resources and games to play with students. Although these links seem to focus mainly on mathematical concepts, many also relate to a variety of other subject areas and make learning fun.
This is a website that provides many different lesson plans for all subjects. You can get so many different ideas for your class and lessons. I used it specifically for Geometry and it gave some great lesson plans.
This is a site that has different posts and online discussions with other teachers around the world. As a future teacher this would be very helpful to see what works and what does not always work for some teachers. It provides different ideas for all teachers and is a great resource.
This website gives different interactive games and puzzles that teachers can have the student use for extra practice. It includes many different topics including probability, algebra and geometry.
This website is great when needed to reference anything dealing with Geometry or Trigonometry. It provides links to different properties of shapes, which is great for kids! The website also provides explanations and definitions when trying to find the area or perimeter of a geometric figure.
This website is filled with standard-based math activities for the teacher to use in their classroom. Each month the website picks a few of the lesson plans that will fit well into the classroom. They seem like they can be easily adjusted for any grade.
Teaching resources for mathematics teachers, a question and answer service for teachers and students, careers of mathematicians, a problem of the month and more.
PBS kids is just great. This website URL will take you to the games section for kids. It does require a user name and password however instead of instant use.