Extremely useful for NDS Lite owners - it's not always possible or convenient to use the power adapter to charge your DS Lite, but with one of these cheap cables you can charge it from any USB device - whether your computer or home or car USB transformer. One less thing to cart about or find a plug socket for! Since I got one of these I've never used the plug-in transformer - it's just easier to use this cable with my computer, whether home or away.
There are several versions of these available from DealExtreme (and elsewhere). See first comment for list of cables and clickable links. Cables for charging the original DS, DSi, PSP and combinations also available at similar prices, including delivery.
DealExtreme are in Hong Kong, so it takes about a week for stuff to arrive after they ship it (in my experience they ship pretty quickly. but sometimes they take a week or ten days). They take Paypal too, so no credit card worries - you don't even have to set up an account - they get the details with Paypal Express Checkout.