Yoshi @ # 1!

Yes, As simple as that
make a game, do anything that can use touch screen, put it into a DS Box
then -voila- it prints money...

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The Japanese top ten follows, with weekly sales figures:

1. Yoshi's Island DS / 303,114 DS

2. Monster Hunter Portable 2 / 93,099 PSP

3. Layton Kyoujo no Fushigi na Machi / 45,344 DS

4. Kenka Banchou 2: Full Throttle / 42,131 PS2

5. Super Robot Taisen W / 36,310 DS

6. Wii Sports / 35,298 Wii

7. Gundam Musou / 31,145 PS3

8. Dragon Quest Monsters – Joker / 26,452 DS

9. Wii Play / 26,340 Wii

10. Motto Nou o Kitaeru Otona DS Training / 20,716 DS

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source: Japanese charts: Yoshi sells over 300k in first week