There is nothing more epic than Mahler for >10 minute songs. He's the grand master of it.
There are so many good songs of decent length. I much prefer these to the 3:45 shit you hear normally. I feel kind of like Si in the beer thread - overwhelmed by what to talk about. Most recently I've been revisiting Godspeed You! Black Emperor and Sunn O))), although I don't know if I'd call them epic. I'll post more later, but in the mean time I'll just leave you with It's a Fast Driving Rave-Up with The Dandy Warhols Sixteen Minutes. That shit right there is pretty epic for me.