Oh oh I'll try to think of a few.
Koi ING - just because it's one of my favourite songs. Also, since the current Momusu is 9 members (is it??) they could make 3 versions of it, with every time different 3 girls as the leads :3
Dokusen yoku - especially for the rapping parts
Otome no shinrigaku - because somehow I can see this song having a funny PV
Say YEAH! Motto Miracle Night - when I became a fan I thought this song was a single, and I was so disappointed to find out it wasn't... And the PV would probably be cool, all futuristic and stuff
Berryz's HA HI HO song - it'd be funny, for sure
Nacchi's Toumorokoshi to sora to kaze - loved the CMs, and I really wish they had shot a PV for it, too
C-ute's Wakkanai(Z) - well, it's their only indie without a PV
In my top 3 favourite C-ute songs, as well
Indigo Blue Love for the Reina, Eri and Risa fans
Alright, that was some random songs