This site is FULL of fun math puzzles. They vary in difficulty, some are easy word problems, others are really hard, and some are riddles. Older grade schoolers would get the most out of this site. There are four links to other Puzzle Ring sites that are good as well. The downside is that to obtain the answers you have to send a new puzzle to add to the site.
Access is fast, and the site downloads quickly and is always available.
The answers to the previous week's puzzles are posted every Thursday. The problems are categorized by grade levels. The problems are for kids in grades 3 and up. For those parents that need help helping their kids, this page has a Parents' Hand book. The link called Project Watch has online math projects that teachers are doing.