If you don't already own a DS this is a superb buy. The DS is currently leading the console wars, its outselling all other hand held and home systems and if that isn't enough to get you interested how about this...
The DS features stereo sound, a microphone to interact with games by blowing to help start a fire (Lost in blue) or blow away clouds (Yoshi touch and go), and even speech recognition (Brain training).
The DS features unique touch screen controls which game developers are taking full use of, for example performing operations (Trauma centre) or playing sudoku! The DS also features 2 screens which can be useful for playing on one screen while viewing a map or stats on the other screen.
So you already own a DS and don't think you need a DS lite? I once had the same view, that is until I held a DS lite, its lighter, has varying backlight settings which are much brighter than the DS or PSP. This time around the DS lite also features an improved stylus which is longer and thicker.
Once you play a DS lite you'll understand why you should buy it, if you own the old DS you'll see why you should upgrade! You'll then be left with a spare DS which can be used to link up with the WI-FI connection which will enable you to play against other players. Many games now even feature a 2 player mode with only 1 cartridge while the 2nd DS will download the multiplayer option.
What else could the DS possibly need you ask? Well it also features internet access to play against player's world wide on games such as Mario Kart and Animal Crossing. There are also download points in various shops where demos can be downloaded to test a game before you actually buy it, or even downloading new packages for your current games! Picross allows owners to download new puzzles to extend the games life.
Finally the future for the DS is also looking pretty good, with connection options to the Wii, the possibilities will be endless!
The only reason I brought a white DS rather than a black one is because the black one gets full of finger prints and greasy marks! If your into keeping your DS nice, shiny and spotless i'd recommend the white version.