I haven't read that many gag manga, but I've laughed a lot of other series.
Beelzebub is probably the funniest I've read. One Piece is also pretty funny, but not often enough. Yotsuba&! is funny too, but in my opinion it's more entertaining and cute.
Just started reading Arakawa Under the Bridge, and I must say it got some hilarious moments!
I've also read a little of Gintama, and I thought it was very funny. Don't know why I stopped reading actually.
I don't know if it was mentioned already,but Kinnikuman is hilarious!
Just like Nichijou.You should watch the anime adaption.It's epic win!
I'm a little dissapointed by the amount of times between scans but the first two chapters of Yondemasu yo, Azazeru-san were hilarious. If nothing else, I recommend watching the anime.
Ust just mentioned Bobobo,how could i have forgotten about that?Hilarious Weirdness and Randomness.
Sket Dance - Well, I re-read it few time, and still, i laugh at it ~
Mikuni Shin's Life of Hunter (Monster Hunter Orage Omake) - It's really funny in my opinion XD I wish Mikuni makes more omakes XD
Arakawa under the bridge and Ranma 1/2 were the best gag manga i've read.
Code:breaker and Midori no Hibi has some funny chapters too. (those few funny chapters got me rofl)
Also, on my list are Fullmetal Panic! Comic Mission, and Ouran high school host club even though the latter one is gender bender.
Hmmm, Gintama is probably my number 1 gag manga. Sket Dance, Hayate no Gotoku!, & Arakawa Under The Bridge also appeal to me too.
if your looking for a gag manga that also has a good story line then i think that sekirei is a good choice or ichigo 100% although that gets more serious as it goes on but it's still an awesome read
Sket Dance is my favourite comedy manga and Arakawa Under The Bridge my favourite comedy anime. I'd include Gintama as one my favourites as well, except I'm pretty behind (I really need to catch up).
Has anyone read Binbou-gami? I heard that it's pretty funny and Sunrise is planning to use its anime adaptation as a replacement for Gintama at the moment.
Hayate the Combat Butler
Full Metal Panic!? Fumoffu
Arakawa Under the Bridge
Danshi Koukousei no Nichijou
I'm currently in love with Joshiraku because it has the same writer with the author of Sayonara Zetsubo Sensei, and its heavy use of Japanese puns and cultural reference. The scans is a little bit delayed, I recommend you to watch the Anime if you think you would like it.
Well the funniest manga I've ever read are Gintama, GTO and Shonan Junai Gumi. All of them are hilarious. And all of them have their own unique style. But it's not only the comedy the serious moments are also marvellous and I really enjoyed/ enjoy reading them.