I like my Lite and can't say anything for the DSi. If I were upgrading I'd get the DSi XL/LL. I suppose it might not appeal to all, but the screens look a little better and are much larger. I'm not really the type that needs to throw the thing in my pocket so I'd be all over it.

DS Lite will be the cheaper option. Also keep in mind the 3DS is coming sometime. I'd suggest getting the charger from Amazon and waiting to see how things pan out. If you absolutely can't wait I would keep in mind that there are some games starting to make promising use of the DSi's camera.