I was out scouring the shops today and discovered that Knex do mario kart "lego" sets. There is a marion one and a yoshi one. I saw them in Forbidden Planet but I imagine they are available on the internet.
They also had Mario ds cases, Mario ds stylus pens, mario key rings, various plush Mario related toys (I felt obliged to buy Bowser 
), Mario calendars and small plastic mario figures. I didn't buy all of these things but thought it might help those, like ourselves, living with Mario obsessed children.
I also saw a pack of cards in Waterstones, I think they were Usborne ones, of optical illusions. Ds is fascinated by optical illusions so they caught my eye.
Hawkins Bazaar and Paperchase had little pots of what looks like some sort of play doh or putty with alien/monster eyes and limbs that can be stuck in the blob. They were £6 so quite expensive for what they were but they looked good fun.
They also had snaps for 50p a box. I wasn't sure if these were a good idea or not.
I will try to remember what else I saw.