I like brain training and more brain training. I also like deal or no deal and I am also a bit partial to cooking mamma
There is lots of stuff out there for adults now- I guess it really depends if you have bought it to mess around on or if you are wanting to keep your brain active.
Someone I work with has one of the 'games' that helps you cook and she has had the learn spanish which she said was good.
I had a DS but got bored of it after a few months.