I'm not an avid MM listener. I'm not into the whole Momusu/ Hello! Project phenomenon.But I can give you some information about them. Morning Musume [can be translated as 'Daughters of Morning'.] is a popular all-girls idol group under Hello! Project [a.k.a Tsunku's army.].The line-up constantly changes when new auditions are held and an 'generation' of new girls are picked. Or when a girl leaves or 'graduates'. Here is the current line-up:

Ai Takahashi [leader]
Risa Niigaki [sub-leader]
Eri Kamei
Sayumi Michishige
Reina Tanaka
Koharu Kusumi
Aika Mitsui
Qian Lin [Linlin]
Li Chun [Junjun]

You can consider them 'bubblegum pop', but their music often touches upon various of genres. As for my recommendations, vocally, I prefer the first and second generations. [the line-up between 1997-1998] They did pretty amazing harmonies back then.

First Generation: Yuko Nakazawa, Aya Ishiguro, Natsumi Abe, Kaori Iida, Asuka Fukuda
Second Generation: Mari Yaguchi, Kei Yasuda, Sayaka Ichii
Third Generation: Maki Goto
Fourth Generation: Ai Kago, Nozomi Tsuji, Rika Ishikawa, Hitomi Yoshizawa
Fifth Generation: Ai Takahashi, Asami Konno, Makoto Ogawa, Risa Niigaki
Sixth Generation: Miki Fujimoto, Eri Kamei, Reina Tanaka, Sayumi Michishige
Seventh Generation: Koharu Kusumi
Eighth Generation: Aika Mitsui, Linlin, Junjun

I divided the PVs in generations. Here's the list:

Ai no Tane
Morning Coffee

Summer Night Town
Daite Hold on Me!
Memory Seishun no Hikari
Manatsu no Kousen
Furusato

Love Machine
Koi no Dance Site

Happy Summer Wedding
I WISH
Renai Revolution 21
The Peace!

Mr. Moonlight ~Ai no Big Band~ [This amuses me. xD Yossie looks good in a suit.]
Souda! We're Alive
Do it! Now
Koko ni Iruzee!
Hyokkori Hyoutanjima
As for One Day


Shabondama
Go Girl ~Koi no Victory~
Ai Araba It's All Right
Roman ~My Dear Boy~
Joshi Kashimashi Monogatari
Namida ga Tomaranai Houkago
The Manpower!!!
Osaka Koi no Uta

Iroppoi Jirettai
Chokkan 2 ~Nogashita Sakana wa Ookiizo!~
Sexy Boy ~Soyokaze ni Yorisotte~
Ambitious! Yashinteki de Ii Jan
Aruiteru

Egao Yes Nude
Kanashimi Twilight
Onna ni Sachi Are
Mikan
Resonant Blue

And their latest PV:

Pepper Keibu