Even though they've been around for about 10 years, I just started listening to Porcupine Tree. They play some very etherial and intricate music. Fascinating lyrics (and they can really sing!) and the recording quality is excellent. They also release on vinyl.
Adrian Belew and Robert Fripp opened for them a few times on their last tour. That will give you an idea what camp they are in. This is not mindless rock n' roll.
Here are the albums I own:
(I've made a killer collage CD from them)
1. Deadwing - Approachable, melodic. A great intro to their newer music. Nice blend of acoustic/electric.
2. In Absencia - Also very approachable, melodic. Newer stuff.
3. Signify (My fav)- Dark, dreamy, melodic, eerie. If you buy this, make sure to buy the 2-CD version. It has some remixed/remastered songs in addition to the originals.
4. Sky Moves Sideways (My least fav of the four) - If you like early, abstract, Pink Floyd (Ummagumma), you won't be disappointed. Spacy and fragmented (to me anyway). This is a 2-CD album.
If you're hearing them for the first time, try Deadwing or In Absencia.