Okay, I'm not an expert on Devin Townsend, but I've got a reasonable amount of knowledge, and have heard a fair bit of his output. So, here we go:
First of all, the band that Devin rose to attention with is the rather heavy (and smart-assed) Strapping Young Lad. In general, they can be a little too heavy for my tastes, and I've only heard two albums and bits and pieces of others, but I'd say City is an excellent album. It's (probably) worth checking out, though I might be wrong: I haven't heard it in a long time, and I don't have a copy available anymore.
Detox (from City)
The song is pretty non-stop the whole way through, though it does become a tad more melodic about 3mins in. Heh.
Outside of Strapping Young Lad, Devin's got a ton of albums to investigate. First of all, after Terria, Ocean Machine would be worth checking out next. It's probably his best solo album: it's very epic, packed full of atmosphere (with a fuzzed-out, shoegaze-ish vibe), and has some very excellent songs. Like Terria, I think it ends particularly strongly, with a suite of three songs that take up thirty minutes of the album's running time.
Really had trouble picking a song to represent this album, but this song seemed like a decent choice: the second half is absolutely loaded with harmonies, too.
Then there's the utterly deranged Infinity, with songs ranging from almost normal pop-metal, to a ridiculous Broadway number, a brilliant circus-y metal song, a particularly speedy song about ants, and some really, really weird stuff. The album also starts with a great instrumental, Truth, which is definitely worth checking out.
Bad Devil (from Infinity)
Once the song gets going, it's fantastic... just stick with it!
Physicist is often considered the worst Devin solo album, and I haven't got a copy of it around, but I do remember some pretty cool songs on it. It's basically a more hookier version of Strapping Young Lad, with the same band members.
Kingdom (from Physicist)
Sure, it's loud and abrasive, but it's pretty melodic, and has a monstrous chorus.
Then there's the pair of ridiculous concept albums: Cooked on Phonics (released under the psuedonym Punky Bruster) and Ziltoid the Omnisicent. The former is about a death metal band who sell out and become a punk band because "they were making no money": it's full of silly generic pop-punk songs, amusing between song banter, and narrated by a ridiculous, lisping Devin. Ziltoid is even sillier: I haven't heard it, but it involves an alien travelling to earth looking for a really good cup of coffee. Because it powers his weaponry. Or something.
There's also a new-age-y ambient album, The Hummer, but I haven't heard it, and I'm not in a hurry to, either.
Aside from Strapping Young Lad, Devin also had another band, The Devin Townsend Band, which was supposed to be a separate, stand-alone band that would focus on the less angry/aggressive side of his music. They released two albums, Accelerated Evolution (almost a "normal" metal album... it's grown on me a lot, and is currently a bit of a favourite) and the rather proggy Synchestra (it starts strong, but it's very lengthy, and I found it a real chore to sit through even once).
Traveller (from Accelerated Evolution)
Terrible fan made video, and it seems to be a different / longer mix of the song.
Finally, a few years back, Devin burned out, disbanded both Strapping Young Lad and the Devin Townsend Band and went quiet, only releasing the aforementioned Ziltoid album. Just this year, he's returned with the The Devin Townsend Project: a series of four themed albums, dedicated to different aspects of his music. So far, only the first one, Ki, has been released. It's very quiet, and has lots of "open space"... I'm a little disappointed by it, to be honest. The upcoming Project albums also include Addicted, the poppy-metal album, and Deconstruction, the ultra-heavy album (that's also supposedly a musical (?!?)).
There's a proper video clip for this song, but the audio is far too soft. This version will do.
And that's enough from me.
*Phew*