For computer time we are currently using abcya.com. This sight has some great activities for the kids and it is also kid friendly (no pop-up adds, etc.). Comment if you have a great sight that your students like to frequent!
The following are links to the activities I have created for my kids. Click on the pink link to download the documents for free :)
Roll dice for sum, find equation nearest to your piece that matches the sum.
I printed these documents, framed them in cheap Dollar Tree Frames and hung them in our math area. We write on them with dry erase marker....I love them!
For this activity, enlarge playing board. Each player takes three erasers, tosses them, and adds the numbers together.