Since I saw one of the posts of my friend here Pickle-san, where she showed one of the videos in which Bleach seiyu are actually... singing! Yeah, that is probably common by now, but I just recently watched, I think almost all of them.
And let me tell you, it goes from those that are just SO funny to those are that are just GOOD!
Seriously, most of them are quite good~! They usually sing opening and ending songs of Bleach and many of them are in similar pair as from the anime (like Aizen and Hinamory, Hisagi and Tousen, Rukia and Orihime and so on...) while there are also many solos, most hilarious to be the one of Kenpachi, to some really good ones like Ichigo one, Unohana and Ishida as well.
OH YEAH, funny thing is that the one of Hitsugaya and Matsumoto is singed both in female voices, because well, Hitsugaya's seiyu is a girl. And believe me, in the song she has quite a nice voice unlike the deep and strong voice in the anime. Wow, that some hard core stuff.
The same the fact that the famous character Goku from DBZ was voiced by a girl as well in the Japanese version. Japanese voice actors sure are something.^^

My most favorite song of the pair is the one of Nemu and Mayuri. Yes I know, it sounds weird. But let me tell you, it is quite good!

This ones is just hilarious, but not bad as well.^^

Be sure to check the other ones as well~! :D