What You Don’t Know About Me Could Fill A Book (http://locknkey.livejournal.com/53984.html)
Dean is a lot smarter than Sam gave him credit for. Once Sam figures that out, Dean holds a whole other layer of fascination.

or

the genius who hides in man's tormented soul (http://veronamay.livejournal.com/751915.html)
Dean reads. Sam likes it. A lot.

xxx

That first one is it! Thank you so much for helping me find it!

you are most welcome, enjoy the re-read :)

xxx

Smart went Crazy, Truth went Trendy (http://queenklu.livejournal.com/35935.html) by queenklu
Sam realizes that Dean is smarter than he'd realized, and that it turns out he has a smart kink. There's a funny seduction scene taking place as Dean recites the Seven Wonders of the World. There are little timestamps and alternate views included in the Comments section.

And I think this one might not exactly fit what you're looking for, but it should be close:

Loyal Constituency (http://supernaturalfic.livejournal.com/1596992.html) by girlguidejones
Summary: It's election time, 2005, and Dean wants to vote. Yeah, that's right. Dean.

I really recomend Conversations by Aetheruk
http://samdean.archive.nu/viewstory.php?sid=508