I love Delicious. I have used Delicious for a year now, keeping track of my bookmarks in one spot. I have a friend that uses Delicious in her classroom for webquests for her students to follow. She also find online games and tags them with the names of topics that are being covered, so students have extra practice that they can do at home.
Two of the sites that I have bookmarked in Delicious are:
1. Manga High http://www.mangahigh.com/en_us/ Great motivational math games over a variety of topics
2. Math Bits High School Resources http://mathbits.com/ Caching