Hi, I'm looking for a manga that has the main male lead being smart, most particularly seinen or shounen.

First one that comes to mind is Death Note if you haven't read it already.

Spiral: Suiri no Kizuna
Death Note
Matantei Loki
Mx0

Of course the degree of intelligence differs and they are smart in different ways but one might suit you.

The pen is mightier than the sword...and considerably easier to write with.

Quote from CuthienSilmeriel

Spiral: Suiri no Kizuna

Acc, I've been beaten 😛 . I highly second this.

Also:
ES
Vampire Juujikai
Hikaru no Go
Shin Angyo Onshi

What I like in Trivial Pursuit style. Pick your category:[img]http://i379.photobucket.com/albums/oo233/Reid4891/Manga/trivia-1.jpg[/img]

Ryuuroden
Kiseiju
Historie
Jojo's Bizarre Adventure

This week's favorites:

• Golden Kamui

ççççççç[Ô.Ô] tsutopodus© will eat your manga and steal your cats!

• Detective Conan (Case Closed)
• Cromartie High School (kinda...)
• Fullmetal Alchemist
• Ghost Hunt
• Konjiki no Gash Bell
• MPD Psycho
• Monster
• Pluto
• 20th Century Boys (maybe...)
• Muhyo & Roji's Bureau of Supernatural Investigation
• Mushishi
• Nodame Cantabile
• Yu-Gi-Oh (kinda...)
• Buddha
• Ode to Kirihito
• MW
• The Drifting Classroom (kinda...)
• Metro Survive
• Vagabond (kinda...)

Do note that im making segestions on series with a "smart" type of main charcter, not a "genius" type that im pretty sure that alot of people are going to asume that thats what you mean, altough some of the series that i listed does have a genius type of main charcter.

I'd say Majin Tantei Nougami Neuro.

[img]http://i56.tinypic.com/acfmfo.png[/img]

Seinen :
Master Keaton
Cesare

Shounen :
Kindaichi Shounen no Jikenbo
Houshin Engi

[img]http://i75.photobucket.com/albums/i285/yuuri097/Hanashizume_no_Utage.gif[/img]

Bakuman even has two smart male protagonists

[img]http://img.userbars.pl/69/13603.gif[/img]

I second Houshin Engi one of my faves and the main character only acts dumb but is super smart.

I second Detective Conan, and add Crying Freeman and Ah my Goddess to the list

Sarcasm just doesn't work over the internet.

Death Note
Code Geass: Lelouch of the Rebellion and all the other code geass
Bloody Monday kinda...
ES

Negima
Defense Devil
Gamble Fish
Kami no Mizo Shiru Sekai

Majin Devil- Super genius nerd fights Majin (demon-like monsters) using mostly just his wit, but also sometimes relying on the majin inside himself, which is also trying to take over his body. I like this one because the main character actually solves problems using his brain, Where as most in this genre have the plans always going awry, and solve everything with brute strength. The description doesn't say it but there is also a light romantic element, nothing serious but it's implied he has feelings for the first girl he saves, who becomes his sidekick sort of.

Favorite Manga:
Yu Yu Hakusho
Mx0
Midori no Hibi
That is all.

Swot
Aflame inferno
liar game
Zennou no Noa - The World of Lostmemories

[img]http://i1096.photobucket.com/albums/g325/Gen3r0us/2n0vtwo-1.png[/img]