Amazon has been offering a DS Lite, any colour game for £109.99 for a while. However their current selection of games you are allowed to bundle with it isn't too vast:http://www.amazon.co.uk/gp/feature.html?docId=1000169843
Amazon previously offered a far wider selection though:http://www.amazon.co.uk/gp/feature.html?ie=UTF8&docId=1396201
This post is because the older offer which claimed to have expired at the end of January is in fact still valid. Using that code (DSLGAME9) I was able to get a DS and Mario Kart DS for £109.99. (which is not possible via the current offer)
I also went through Nectar eStores which if it works would give points equivalent to 1% cashback but apparently it takes almost a month to know whether you have been awarded them so that would be a bonus if it works.