If you've never played Chrono Trigger then it's about time you did. For my money, this classic JRPG is one of the best games ever made, and presents probably the most intricate and competent story ever told by our medium. So far, at least.
CD Wow are currently charging £16.19 for the NTSC version, which is compatible with all DS consoles but not with European 3DS units. Bear this in mind.