I am another Dean/Sam girl who likes to sample other pairings at times and especially Dean/Castiel. I mostly read AUs (human!Cas/not a hunter!Dean) nowadays and you didn't say if you like that kind of fics or not so I'll give you only a few recs that are pretty much classics : Peanut butter pumpkin wedding cake (http://sparseparsley.livejournal.com/8666.html), We became fans of collisions (http://community.livejournal.com/her_own_write/29507.html) and Asunder (http://archiveofourown.org/works/62115?view_adult=true). I'm not sure about who bottoms or who tops, sorry. I only really enjoy top!Dean but if I'd let that always stop me I wouldn't read much in this fandom ;)

The other authors, who often write both canon Dean and Castiel as well as AUs (and some Jensen/Misha), that I've enjoyed the most are, in no particular order, FayJay (http://archiveofourown.org/users/FayJay/works?selected_tags[]=27), trinityofone, CloudyJenn at cloudy_fic, olympia_m, strangenessandcharm (http://strangenessandcharm.dreamwidth.org), bauble, janie_tangerine, rockstarpeach, Orphan_account (http://archiveofourown.org/users/orphan_account/pseuds/orphan_account), blue_fjords, entangled_now, thevinegarworks, gedry... Many great writers for this pairing too !