From
http://www.j-cast.com/2010/12/10083206.html :
CD Rankings of 20101. 「Beginner」 947,179 - AKB48 10/10/27
2. 「Heavy Rotation」 709,342 - AKB48 10/08/18
3.
「Troublemaker」 698,542 - Arashi 10/03/03
4.
「Monster」 696,022 - Arashi 10/05/19
5. 「Ponytail to Shushu」 657,868 - AKB48 10/05/26
6.
「Hatenai Sora」 649,339 - Arashi 10/11/10
7.
「Lφve Rainbow」 618,614 - Arashi 10/09/08
8.
「Dear Snow」 590,150 - Arashi 10/10/06
9.
「To be free」 516,142 - Arashi 10/07/07
10. 「Chance no Junban」 471,242 - ABK48 10/12/08
The numbers aren't up-to-date (as can be seen from the Chance no Junban sales), but this confirms that AKB48 and Arashi have dominated the sales of 2010 (since I rather doubt any other artist will be able to pull out such numbers between now and the end of the year).