Einhard

D-Frag - seriously one of the funniest gag manga ever made, random plot, outstanding characters but not for everyone as it seems randomness and some references may be too much for some

Yotsubato - cute, light manga for everyone (age, gender doesn't matter), it's impossible not to laugh reading this

Tokyo Crazy Paradise - one of the best manga overall and it has many hilarious moments (NAKAMURA Yoshiki creates probably the funniest deformed form in the world)

Medaka Box- you either love it or hate it, not for everyone

Fujimura-kun Mates - another great gag manga with a nice feeling to it, recommendation for everyone

Full Metal Panic! - start of the series and FMP Fumoffu anime are just plain hilarious

Arakawa Under the Bridge - one of those wtf I am reading mangas but don't be deceived, after all this years I still believe there is a normal plot deep inside and everything can be explained rationally (or not?)

Sora no Otoshimono - it has great hilarious comedy moments but there are also some really serious parts mixed in between those, it's not pure ecchi comedy as it may look at first glimpse but still one of the funniest out there

Mangaka-san to Assistant-san to - ecchi harem 4-koma, which isn't real 4-koma most of the time, will make you laugh on every chapter

Yandere Kanojo - another great 4-koma, has really funny gags, nice read for everyone 

B Gata H Kei - even remembering the title made me laugh, dirty jokes everywhere, probably only for older readers

every one of this mangas is the funniest in different way