I am preparing by continually seeking out new sites that I can use in the classroom. I find them on other people's blogs, but I get most of my great places from people I follow on Twitter.
I have mentioned Sumdog before. (I. love. Sumdog.) My students used it the other day on the mobile lab, and they were thrilled to be playing against each other. Once the kids become more adept at things, I plan on assigning Sumdog minutes for homework sometimes. The site graphs student progress, and it allows students to choose what game they want to play. Above I was preparing to face off against MarlinL
Another great one I have found and used in the classroom is Thinking Blocks. It is a great visual tool to support kids when doing story problems. It goes along well with our Everyday Math series, too.
Everyday Math site is totally aligned with our series (since it is part of Everyday Math). This is another great resource to use when instructing. you can set the background and use it as you wish. The background set here is for addition facts.
I hope that you find a use for one or all of these sites with your kiddos!