Nintendo has announced that it is dropping the prices of the DSi and DSi XL in North America starting September 12.  Soon you'll be able to snag the units for $149.99 and $169.99 respectively.  The price of the DS Lite isn't changing, while the original model DS has long since been discontinued.  I'd quote from Nintendo's press release, but you're pretty much caught up and probably don't want to read the marketing spin.  Oh, what the heck.  It's tradition!

"We know shoppers want to get the maximum value out of every dollar they spend," said Cammie Dunaway, Nintendo of America's executive vice president of Sales & Marketing. "Our new Nintendo DSi prices make it easier than ever for consumers to access the tremendous variety of games, applications and social tools on the Nintendo DSi and Nintendo DSi XL systems."
 
The Nintendo DSi and Nintendo DSi XL systems offer consumers access to more than 1,300 packaged games and more than 200 downloadable games. Both systems feature two built-in cameras and photo- and sound-manipulation software that provide for a more social experience. Users can wirelessly upload photos to Facebook with the touch of a button (wireless broadband Internet access required). The Nintendo DSi XL system, which features a screen that is 93 percent larger than that of the Nintendo DS Lite, comes pre-loaded with software like Brain Age™ Express: Math, Brain Age Express: Arts & Letters, Flipnote Studio™, Photo Clockand the Nintendo DSi Browser.

Consider some friendly advice before you rush out to the store on the twelfth.  This price cut has to be a pre-response to the upcoming release of the DSi's successor, the 3DS.  If you don't already have a DSi, hold out for the new machine.  It'll cost more than a DSi, yes, but you'll be better off in the long run.  Now, if I may speculate: if the DSi is getting a price cut now, doesn't that make you wonder if the 3DS's release is closer than we assume?  It's almost as if Nintendo is trying to clear out some stock before the next big thing shows up to steal last generation's thunder...