One of my favourites by Herself is "Spike's Girl," which can be found on Herself's website and also fits your criteria.
I also recommend "Cast Me Not Away" by EnigmaticBlue:
http://www.freewebs.com/enigmaticblue/cmna.htmIt's not actually post-"Chosen" or post-"NFA," but it has lots of angst. To summarize, Spike leaves Sunnydale after Buffy beats him in "Dead Things" and builds a new life for himself in LA. When something life-changing happens to Buffy, she seeks him out to make amends. Also includes Wesley and an original character as leads.
And lastly, "Hallelujah" by Holly:
http://paragon.dark-solace.org/stories/hallelujah.htmI wouldn't call it angst, exactly, but there is a lot of Buffy and Spike dealing with their issues after NFA.
Enjoy!