Mathemagic

Hey all,
Got given iphone credit for my birthday and splashed out on this (usually stick to free ones!). Some interesting little tricks that might be fun as starters etc for lessons. Here's one that I particularly like:

To multiply two, two digit numbers e.g. 19 and 17

Take the units place digit of the smaller number (7) and add it to the larger number (26). Add a zero (260). Now multiply both ones digits (9*7) (63) and add it to the 260 (323) and thats your answer!

I'll just do another in case its not clear e.g. 11 and 16
Take (1) and add it to 16 (17), add zero (170). Then 1*6 (6) added on gives 176 as the answer!

Anything anyone else has come across thats fun? I like to use as many interesting things I can to help students develop some interest (they often hate it by the time they get to secondary school!)