Since it was posted in the NPD thread, will post it here, too.
U.S. 3DS All-Time Download-only Sales (until April 18 ~9:30 EDT)
Note: Bundled/Ambassador games are not included. Basically just anything you had to click on 'purchase' button to get that at some point in its life cost money.
1. Pokemon Dream Radar
2. Pushmo
3. 3D Classics: Kirby's Adventure
4. 3D Classics: Kid Icarus
5. Colors! 3D
6. Pokedex 3D Pro (the on-going sale probably pushed it over FE)
7. Fire Emblem: Awakening
~80K
8. New Super Mario Bros. 2
9. 3D Classics: Xevious
10. Sakura Samurai: Art of the Sword
11. Bird Mania 3D
12. Mighty Switch Force!
13. Dillon's Rolling Western
14. Luigi's Mansion: Dark Moon
~50K
15. 3D Classics: Excitebike
16. VVVVVV
17. Let's Golf! 3D
18. Gunman Clive
19. Mutant Mudds
20. 3D Classics: Urban Champion
Do we know what Pokemon Mystery Dungeon did in retail in March? That'd provide at least a lower limit to this chart, since it was 145K March retail + LTD (presumably) digital as of yesterday.
May try to do this download-only, all-time chart to coincide with NPD results, since Nintendo's feeling happy about giving out digital numbers in the U.S. currently.