To follow up, I've noticed that a number of brand-new albums are now streamable (handy!), as well as fairly recent albums from obscure artists, or at least artists I've discovered through using Last.fm.
So here's an additional list of streamable albums, mainly for my own use but maybe useful to other users as well. If you're in the mood to try something new, these are all worth checking out.
Röyksopp - Junior
Yeah Yeah Yeahs - It's Blitz!
Cut Copy - In Ghost Colors
Why? - Alopecia