There are some really good epics on here! I have a mini-list in my Recommended Reading - it's mostly slash, but there's some het; I'm putting the list of them on here, edited to include only the long ones.
ORIGINAL M/M:
Obsession - Mitts (M/M)
Fiend by the Bay - Bean Montag (M/M) - basically anything by Bean Montag is epic and amazingly written.
The Crescent Sky - Bean Montag (M/M, wolf)
The Crescent Sky II: Blood Moon - Bean Montag (M/M, wolf)
Slack Water - Bean Montag (M/M, wolf & attaches to the Crescent Sky Series)
Between Night and Day - Bean Montag (M/M, wolf)
The Last Pure Human - TwistedHilarity (M/M, xeno/fur) - more quirky, but quite amusing!
November - Kabi (M/M , mpreg)
Cadet Murphy - Kaby (M/M, mpreg)
August - Kabi (M/M, mpreg)
We're Never Balanced - MisterVix (M/M, mpreg)
Tentacles for the Brides Bouquet by Kiix (M/M, mpreg, xeno?/fur) - effed up, but it's amazing.
ORIGINAL M/F:
Bad Moon Rising - Gatsby (M/F, wolf)
Lecture Notes - sheherazade (M/F)
Lalama - Pure Intoxication (M/F)
RECS IN OTHER PLACES:
1. The Kindred Spirits Series by dolphin (Original) (M/M, mpreg, wolf) containing...
The Sineult Cycle 1: Lost & Found
The Sineult Cycle 2: Bridges
The Sineult Cycle 3: Inexpressible
all at dolphin's page: http://www.angelfire.com/folk/kindred/index2.html
2. The Taming Series (Star Trek) (M/M) by Skazinetilsky Karmen and Ghia, containing...
The Taming
The Taming 3, Version B, Ending A
both at Amothea's Angst Archive: http://amothea.slashcity.com/db/viewstory.php?sid=522
4. The SGA verse series by Xanthe (Stargate: Atlantis) (M/M)
containing...
Coming Home: http://www.squidge.org/peja/cgi-bin/viewst...mp;warning=FRAO
&
General & Dr. Sheppard: http://www.squidge.org/peja/cgi-bin/viewstory.php?sid=23877
at the Wonderful World of Makebelieve
5. The Indago Series by LdDurham(HP) (M/M, mpreg, xeno)
containing...
Indago
Indago: Reborn
Indago: 3
all at LdDurham's Skyehawke dot com site: http://archive.skyehawke.com/authors.php?no=1100