I'd say their whole discography. Kanjani8 shine in variety but their lives are the best.
Though knowing what type of songs you like, I'd say you've got your favorites there. Osaka Obachan Rock, Sukiyanen Osaka, T.W.L, are playful, too. Kanfu Fighting, maybe?
I think the one Nayoko is talking about is Monjai Beat (album song)... or maybe Aoppana... Not quite sure.
Solos -- all the members have solos on albums. Usually on a second disc. As for b-sides... their b-sides usually keep their rock-y sound (which is why they're so awesome) so I don't know if you're into that.
the lives are ½ entertainment and silly stuff and ½ playing the instruments and being the amazing rock guys they are.
The singers of the group are Subaru and Ryo, though. Followed by Okura (drums), Maruyama (base) and Yasuda (guitar). Murakami (piano) and Yokoyama (hand-drums etc) aren't that known for being the best singers, but of course they too have their good and bad days. Though, like I said everyone has a solo each. I doubt they're available for streaming though...
On the top of my head I know these titels (there are at least 2-3 more songs for each person though)
Yokoyama You - WONDER BOY
Shibutai Subaru - A
Murakami Shingo - Forward
Maruyama Ryuuhei - MAGIC WORD ~Boku no nari ni~
Yasuda Shouta - Watashi kagami
Nishikido Ryo - Stereo
Okura Tadayoshi - no-no-no
Good luck finding them though. (>_<)