If you own a DS and you don't own Zoo Keeper you are really missing out. Utterly addictive, it makes long train journeys pass in a blur of cross looking hippos and surprised lions. There are hundreds of puzzle games like this for the DS and really it isn't much different from Bejeweled but it does have an excellent quest/challenge mode and infectious background music!
You can also connect to another DS and play 2-player versus which is a great idea.