Oh... I love first time stories and this is my favorite one... it´s not S07 or S08, it´s pre-Stanford one but... I´m sure you will love it :

1. absolutely awesome bewaretheides15 wrote "Crush" - http://bewaretheides15.livejournal.com/18463.html (http://bewaretheides15.livejournal.com/18463.html)
Summary - Dean looks at him different now, Sam just can't figure out what the difference is.

There is slow buid up and the love they have between them is just suffocating :) Beautiful first time story.

2. another perfect first time story is "Almost At Home" by balefully here : http://balefully.livejournal.com/598931.html (http://balefully.livejournal.com/598931.html)

3. "if we keep living this fast, no one will have time to die" by oxoniensis here : http://oxoniensis.livejournal.com/379020.html (http://oxoniensis.livejournal.com/379020.html)
Summary : First time, falling in love with a side of monster-hunting

4. Really short but really good one is "IT’S NOT GONNA BE JUST ONLY A KISS" by idlehands here : http://idlehands.ponderosa121.com/its-not-gonna-be-just-only-a-kiss/ (http://idlehands.ponderosa121.com/its-not-gonna-be-just-only-a-kiss/)

5. "Rest stop. Near Leland, Mississippi." by merryish you can find on AO3 here : http://archiveofourown.org/works/4208 (http://archiveofourown.org/works/4208)
Summary : A tiny story in which Sam and Dean kiss. For the first time.

6. Another one from merryish "three months | the kiss addiction remix" you can find here : http://archiveofourown.org/works/4203?view_adult=true (http://archiveofourown.org/works/4203?view_adult=true)

7. One beautiful first time called "A road trip down memory lane" by radiophile is here : http://lockthecolt.livejournal.com/33151.html (http://lockthecolt.livejournal.com/33151.html)
Summary : I'd take anything you give me, and you'd give me anything I'd take. | Sam reflects on their first time, back when things were easy between them. (pre-series up to S3)

8. And one absolutelly gorgeous first time "What Lies Between" by Sonny you can find here : http://samdean.archive.nu/viewstory.php?sid=3659

I hope you will enjoy them as much as I did ;)