See Games page also.
Manipulate numeric expressions with this TES resource from Piers Butler.
Make 24, see 4 Numbers Game. For further information see this page on the problem and a link to an online program which optionally shows solutions as well as presenting random problems. The program will also show solutions for any given set of four numbers. If you just want to make a note of a few problems and solutions then you could use this page from ResearchManiacs.com.
Clever tricks such as Multiplication by 11 or Squares Ending in 5 can make good starters, with older students algebra can be used to establish why these tricks work. Mudd Math Fun Facts has a wealth of material which works well in the classroom. More Amazing Number Facts are available from the Madras College Mathematics Department site.
YouTube has various videos which could make good starter activities – see Multiplication With Your Fingers for example, Vedic Multiplication or Russian Multiplication see Activity 6.3 in this CIMT Activities booklet for an explanation of Russian Multiplication.
and see this fuller explanation from Chris Lusto
Broken Calculator from the Woodlands Junior School site. Different levels of difficulty are available.