It will soon be time for World Maths Day 2015!
In the mean time some of these games are good for practise!
If your students enjoy games of this kind Sumdog is free all year round.Manga High is now completely free in several countries including UK, Ireland, USA, Canada, all of Scandinavia and the Indian subcontinent. For other free Number games see this page also this page on games collections; the collections from Math Playground and that from Oswego City School District are particularly good for mental arithmetic. For practise at tables, including against the clock see this collection.