http://www.fontshop.com/fontlist/alternatives/comic_sans/

Thank's for the link chrisherron.

Nice try, but lot's of informal alternatives.
And MBV Pedestria is too much formal...

What's the exhibit for / about? (That kind of marker felt stuff might be appropriate for a kiddie-comics convention or maybe a trade show of elementary school classroom supplies?)

"very close to Comic Sans but a little bit more formal"

I'm not sure you can have both. Either it's going to be close to Comic Sans OR it will be a bit more formal.

For something that's handwritten, I like Mark Simonson's Felt Tip family:

http://www.ms-studio.com/FontSales/felttiproman.html

Tekton, perhaps?

Maybe it's still not right, but Burbank?

(Someday the world may have my Emi, but not yet...)

www.blambot.com

How about Caflisch Script?

I secretly said a little prayer for you because you refuse to use Comic Sans. You deserve to live a very blessed life. :)

Try:
Apple Casual
Happy Sans
Bradley hand
Pea Sue's Print

Perhaps Markup might work?

How about Sauna by Underware?

What about Helvetica Rounded?

I vote for FF Duper.

Uau!!

I was away for a few days and now I'm back I see so many tips.
Thank's to all.

I may not explain myself clear.
I'm not looking for an informal font, or for a kiddie look.
I'm trying to silently change the panel exhibits from Comic Sans to a more serious font.
The earlier designer before me used Comic Sans and the client accepted.
But now that I'm designing new panels and material for the exhibit I would like to evolute to a bit more serious font.
If I radically change the font the font, the client may not like.

From all your suggestion, FF Duper OT Bold may be the one that is more close to what I look for (if there exists...).
For now I decided to use Chalkboard, that is very close to Comic Sans, but the ascenders and stems are not so curvy.

P22 Peanut, Chaparral?

Cronos

ITC Legacy Sans (this one could also be a good replacement for Papyrus)

ITC Highlander