A fan remake for Super Mario Bros. 3 using visual elements from the DS game New Super Mario Bros. is done, and the creator has released a trailer for it. He's calling it New Super Mario Bros 3. A patch will be coming from the DS game this Friday, but you can take a look at the crazy amount of work done so far in this very long video. Of course, you'll have to be down with the flashcard action to play this.
This looks insane and fun. With the rom hacking required, I suspect that Nintendo will be all over it. Keep that in mind if you're interested.