Music/Bands Most Popular In Japan?

I wanted to know for the sake of knowing,but what's popular NOW in Japan when it comes to music?Like Rihanna&Hannah Montana and AKON&Green Day are in America,what bands are THE most popular in Japan?
Please,if it's not too much to ask,no Dir en grey or anything like that,unless it's actually extremely popular....^_^

You can look up what is currently popular by checking out the Oricon Chart (its like the Billboard Top 40 in the US):

http://www.oricon.co.jp/

If you don't read Japanese there are many websites that translates the charts. Here's one I found through google:

http://www.jpopasia.com/charts/