This website has interactive math and reading games that can be played as a class on the smartboard, or individually on the computer. It is very clearly organized by grade, and the games are engaging and fun!
ABCya is a wonderful website that we use at out centers with Pre-K and K ages. It is loaded with free online educational games. The games are mostly math and ELA based and are fun and interactive.
IXL has hundreds of Math related games, categorized by grade and topic. It is a subscription based site, but allows quite a few free uses, and even once you've used up your free practice for the day it refreshes and let you try again the next day.
IXL is the world's most popular subscription-based learning site for K-12. Used by over 5 million students, IXL provides unlimited practice in more than 4,000 math and English language arts topics. Interactive questions, awards and certificates keep kids motivated as they master skills.
This link to the Oxford English Dictionary is an invaluable resource for Middle School ELA and Secondary Ed English teachers. I can see it as a frequent "go-to" site for Student Researchers, providing more interesting content than a standard online dictionary. Because the OED is concerned with word origins, I believe it would be helpful in creating bridges with ELL students as well, giving them a chance to see the linguistic contributions their language has made to ours. Check out the link in the lower center column for teachers and students (resources and lesson plans).