This list is a list of Japan's 50 best selling artists UP TO 2005. So all sells after April 1st, 2005 aren't counted.
All single + album + collection sales in Japan (up to 2005)
From Music Station 2005.04.01 (REAL HAPPY TO SEE GLAY AT #7!)
And for the Utada fans, she's at number 9! Proud :) The list is surely slightly different now though.

Rank Artist Sale
1 B'z 75,614,000
2 Mr. Children 50,635,000
3 Southern All Stars 47,083,000
4 Hamasaki Ayumi 45,528,000
5 DREAMS COME TRUE 40,893,000
6 Matsutoya Yumi 37,790,000
7 GLAY 35,800,000
8 ZARD 35,450,000
9 Utada Hikaru 32,160,000
10 CHAGE & ASKA 31,220,000
11 Matsuda Seiko 29,260,000
12 GLOBE 28,600,000
13 SMAP 28,400,000
14 L'Arc~en~Ciel 25,760,000
15 Amuro Namie 25,750,000
16 Nakamori Akina 25,100,000
17 TUBE 23,880,000
18 Ohguro Maki 21,890,000
19 Every Little Thing 21,630,000
20 TRF 21,500,000
21 Nakajima Miyuki 21,310,000
22 KinKi Kids 20,790,000
23 Nagabushi Tsuyoshi 20,380,000
24 Makihara Noriyuki 19,830,000
25 SPEED 19,280,000
26 Fukuyama Masaharu 18,760,000
27 Itsuki Hiroshi 18,700,000
28 Kome Kome CLUB 18,320,000
29 SPITZ 18,290,000
30 MISIA 17,150,000
31 Yamaguchi Momoe 16,190,000
32 Himuro Kyosuke 15,710,000
33 Inoue Yosui 15,670,000
34 Sawada Kenji 15,660,000
35 Go Hiromi 15,620,000
36 Morning Musume 15,470,000
37 Mori Shinichi 15,400,000
38 CHECKERS 15,300,000
39 Imai Miki 15,220,000
40 Nakayama Miho 14,970,000
41 Kudou Shizuka 14,820,000
42 Koizumi Kyoko 14,230,000
43 Kuraki Mai 14,220,000
44 JUDY AND MARY 14,130,000
45 Matsuyama Chiharu 14,030,000
46 Yazawa Eikichi 13,930,000
47 WANDS 13,730,000
48 T-BOLAN 13,610,000
49 Mariah Carey 13,460,000
50 Takeuchi Mariya 13,400,000