1. Depends what you like really. If I remember your tastes correctly, you should enjoy all three of the latest albums, In Absentia, Deadwing, and Fear Of A Blank Planet. Due to his work producing other bands, Steven Wilson brings a bit of a metal influence into the prog on those albums. The two indra mentioned are the immediately previous albums and feature prog in a more focused setting of songwriting. The earliest albums are quite spacy and I think any Pink Floyd fan (especially if your favourites are Shine On You Crazy Diamond, Echoes, and all of Animals) would appreciate The Sky Moves Sideways and Up The Downstair.
2. Similar? Well, the obvious answer is Blackfield. Musically, there aren't that many similarities to present day Porcupine Tree, but Steven Wilson makes up half of Blackfield and the other half, Aviv Geffen, essentially focuses Wilson's prog tendencies into Geffen's shorter, pop-structured songs.
If you enjoy the earlier Porcupine Tree stuff (or if you just like prog of any kind), Pure Reason Revolution are pretty much essential. A few of their songs have heavier leanings too: Trembling Willows, In Aurelia (from their EP Cautionary Tales For The Brave, also on the European edition of The Dark Third album), and Victorious Cupid (a free single released on their MySpace).
There's the obvious "big third wave prog band" of Dream Theater - Mike Portnoy and Steven Wilson are friends, though Wilson himself does not like Dream Theater's music. While Porcupine Tree is very much about art, Dream Theater are more about technical brilliance, and their latest albums, while heavier, are really fucking crap if you ask me. I suppose if you've always wondered what Metallica would sound like if they were a prog band, Dream Theater's latest album would be right up your alley.
Two other prog bands I highly recommend are Marillion (the first four albums with Fish as the vocalist slay anything later with Hogarth, and anyone who says otherwise is a liar) and Transatlantic. When you're talking pre-In Absentia Porcupine Tree, it's easier to draw comparisons than it is now, as Steven Wilson is incorporating metal influences into prog in a way different to pretty much every other prog metal band out there. Of the prog-metal-by-numbers bands, Circus Maximus's debut album, The 1st Chapter, or Symphony X's The Divine Wings Of Tragedy are probably best - and they demonstrate the power metal influences that many prog metal bands have but that Porcupine Tree doesn't at all.
