Toys R Us is holding its annual "buy two, get one free" DS promotion again starting on Sunday the 22nd, according to the latest weekly ad (as transcribed by CAG denizens). It's a great time for it, too: people getting Guitar Hero On Tour should be able to defray some of the cost by bundling it with two other games. Of course, even if you don't care about On Tour, you can get a great deal on some DS games. We just focused on that because it's new and it's so expensive that any other DS game comes in at an "equal or lesser value."
Guitar Hero is expensive enough that, under the right conditions (purchasing two Square Enix games along with it), you could get a free Square Enix game! Final Fantasy Tactics A2 comes out next week, for example -- $90 for Guitar Hero, FFTA2, and The World Ends with You is a relatively non-terrible deal.