Three DLC packs have just launched for New Super Mario Bros 2 in the North American and UK. The content includes the Gold Rush Pack, Coin Challenge Pack A, and Nerve Wrack Pack, each of which is a few bucks and can be purchased in-game. If you want to get it all at once, a bundle is offered, but with no discount (sad trombone).
Each pack puts you on a time limit to nab as many coins as you can for a shot at a top global leaderboard spot. Especially studious players can track their progress via the official game site.
If you're still hungry for more after all that, another DLC pack will hit at the end of October, and another at the end of November. Judging by the "Coin Challenge Pack A" name, presumably these will contain at least some similar content.