I had a DS Lite in 2008.. and haven't touched it since.
I'm going to slowly play my way through all the good games DS library has to offer ^.^
But first I'll start off with all the pokemon games (Silver --> Black --> Platinum)
Well, Pokemon is always a good place to start off on. Enjoy your gaming time. I just bought Professor Layton 3: The Unwound Future, Golden Sun: Dark Dawn and Harvest Moon: Tale of Two Towns. I haven't played them yet though.