Off the Script (http://jasmasson.livejournal.com/44199.html#cutid1/) is one of my absolute favorites of this trope.

There's also the list at j2_recs which has a pornstars tag.

http://j2-recs.livejournal.com/6307.html

here over at J2 recs is a rec list for porstar AU

Days in Our Lives (http://directors-seat.livejournal.com/2247.html#cutid1) by titheniel & splashpink.

This is J2 and very long. Pretty sure it's in the J2 recs list though, but I thought I'd mention it. I enjoyed it.

Check out Vegas by astolat: http://intimations.org/fanfic/supernatural/Vegas.html
It's Dean/Sam and is awesome.

Do you have another addy for it? There's a thingy says it's got malware attached, and it tried to download something onto my system without me asking it to.

Saw that most of the other comments are J2, so I thought I'd add some Sam/Dean. There's God Made Boston on a Wet Sunday (http://balefully.livejournal.com/617895.html#cutid1), which is teenchesters. John's gone, and Dean figures out a way to make some cash for him and Sam, but Sam finds out.

And, of course, the epic The Bright LIghts of Disturbia (http://archiveofourown.org/works/181007/chapters/266202) begins with Sam seeing a gay porn starring Dean.

Back to the RPF, there's also Best Job Ever (http://rockstarpeach.livejournal.com/109750.html), which is romantically J2, though there's porn with Matt Cohen also. It's rockstarpeach, though, and pretty much everything she writes is golden.