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!