Hello! Project is a very popular name from what I've heard. Hello! Project company holds one of the most popular bands: Morning Musume They have surpassed Pink Lady(a very popular duo in the 70's, the group were claimed to be the most popular record artist in the world at that time). Morning Musume has been very popular since their wonderful sell of 50,000 copies of their demo single “Ai no Tane” in 1997. Morning Musume became a staple of the Japanese music industry. They still are coming out with more and more singles and CDs.
Now, we can not forget the other groups and solo artists under H!P:
Aa!
Abe Natsumi
Berryz Koubou
Compilation Album Tracks
Coconuts Musume
Country Musume
°C-ute
Fujimoto Miki
GAM
Goto Maki
Heike Michiyo
Hello! Project Eggs
Konno Asami
Kusumi Koharu
Maeda Yuki
Matsuura Aya
Melon Kinenbi
Miyoshi Chinatsu
Morning Musume
Morning Musume Sakura Gumi
Minimoni
Nakazawa Yuko
Pucchi Moni
Shuffle Groups
Taiyo to Ciscomoon / T&C Bomber
Tanpopo
Tsuji Nozomi
v-u-den
W
ZYX
Some of these others listed are more popular than others. If you would like to listen to them they are on youtube. Not all, but most.
Here is a site with good color-coded lyrics(not all the groups/solo artists are listed on the site that are listed above):
http://www.projecthello.com/Please Enjoy. *bows*