Just in time for the recent price drop of the DS Lite, Amazon is offering up a buy one, get one half off sale on quite a few excellent DS and 3DS titles. Eight pages of DS titles are covered by the offer, including New Super Mario Bros., Okamiden and Professor Layton and the Unwound Future. Among the 3DS games included in the sale, you'll find Pilotwings Resort, Ridge Racer 3DS, Steel Diver, Super Monkey Ball 3D and the Nintendogs + Cats games.
The sale description warns that supplies for the sale are limited, and that Amazon may pull the sale at any time, so we don't know when it will all end. But it's a nice chance to expand your 3DS or DS library nonetheless.