The Burden of Being Me and You (https://www.fanfiction.net/s/7758453/1/The-Burden-of-Being-Me-and-You) by Aecoris (Gen. AU to season 4. Dean clawed his way out of Hell as a demon intent on stopping the apocalypse and the plans for his brother.)

Catching Hell (https://www.fanfiction.net/s/11395674/1/Catching-Hell) by A Deed Without a Name (Unrelated Wincest AU with hunter!Sam and demon!Dean, but it cleverly incorporates big chunks of canon into the story.)

They're definitely not light-spirited, but it's not all angst and misery either. And Dean's not exactly your typical demon in these.

Thanks a lot, I'll read them right away :)

And Aecoris has two sequel fics to "Burden." The third one is a WIP. Well worth the reads!

Enjoy,
Eleri

I second the Catching Hell recommendation - LOVED that one.

You might also enjoy After the End (http://archiveofourown.org/works/1727609/chapters/3683639) by amypond45. There's definitely some angst, but demon!Dean isn't strictly evil, there's no noncon, and there's lots of great brotherly love and feels.

Thank you!

I haven't read this one yet, but it sounds promising (it says Season10/DemonDean and Season1 Sam, involving timetravel):
Jericho by xxxkia with art by cassiopeia7
http://archiveofourown.org/works/4343036/chapters/9850508 or at LJ: http://xxxkia.livejournal.com/740.html

The Fortress series by glasslogic is a whole new take on demons and hell, very different from canon (DemonDean is postS3 here)
http://archiveofourown.org/series/20086 or on LJ: http://glasslogic.livejournal.com/10886.html

Fade to Black and its sequel Black is the Colour of my True Love's Eyes by runedgirl (also postS3)
http://runedgirl.livejournal.com/45473.html#comment-2351521

Above and Below by vail-kagami has both DemonDean and Demon/BoyKingSam
http://vail-kagami.livejournal.com/146352.html
the prequel (how they got there) is even better (in my opinion): In the Darkness (With You)
http://vail-kagami.livejournal.com/163865.html
both stories are also at AO3 as the (Boy) Kings series
http://archiveofourown.org/series/23594

All those stories are rather dark

Embrace the Change (http://archiveofourown.org/works/1667951/chapters/3540344): I like to call this fic "the better version of season 10", it's really entertaining and has this general "viva la demon!dean" vibe :D

Revenge of the Jedi by borgmama1of5
Gen. Story in 3 parts. Warning: character death.
Summary: "No, Dean, I wouldn't. Same circumstances, I wouldn't."

http://borgmama1of5.livejournal.com/79454.html

Thanks y'all :)