Dopesmoker is freaking awesome, no doubt.
Most of my recommendations are going to be on the dronier side of things, I'm afraid. You've got Absolutego by Boris, it's a classic. I would say it's a patience tester (65 minutes long) but if you're looking for extremely long songs, I think you must have a fair bit of patience. Boris and Merzbow: Sun Baked SNow Cave, another Boris release, also excellent, 66 minutes long, though it's an extremely difficult listen. Also, Boris's Flood release. It's basically a 74 minute long post-rock song, but it's real awesome.
A lot of stuff by Nadja is about 20 minutes long. Possibly not long enough for you, but they're all really good anyway. And Meshuggah's Catch 33 is indeed awesome.
Oh, and freaking Atavist! Real slow crusty sludge stuff, but it's really entertaining. I would highly recommend. Also: Orthodox, another great sludgy doom band. Atavist are a fair bit better though. Finally, there is a really good industrial/drone band called Hyatari (think of a heavier, more riff orientated Jesu) and they did a one song album, which is split into 7 tracks or so. It's called the Light Carriers and it's freaking amazing.
Hope my recommendations helped. I know most of it's real slow doom, but those are the only real long tunes I have.