Keepad Interactive has now got the rights to Mult-e-Maths software and it is now available to customers. Its a great tool to use with either an eBeam or a Graphire tablet. Every time I do a demonstration, teachers are blown away by it's simplicity and ease of use.
You can get a trial of it here.
For those of you who can't get there hands on it - there is another option.
Math playground This has a range of games, manipulatives, and videos that work great on an IWB or tablet.