For
Shakugan no Shana it should fit what you want really, it's a good action/tsundere series, though isn't a really a harem[2, maybe 3 girls later interested in MC] and comedy isn't ussually common.
Also I'll second
Bakemonogatari,
MM, and
Mayoi Chiki they all fit for sure
. And
Kami Nomi zo Shiru Sekai doesn't fit exactly, but it is good.
Other series I'd suggest:
Otome Youkai Zakuro [fantasy, but really it's a series with great development in it and Zakuro is fun tsundere
]
Ookami-san to Shichinin no Nakamatachi
Hidan no Aria[Both of these are action/school based and fit a lot of requirements you want
]
Mayoi Neko Overrun
, and it's very much comedy with school setting]