Most recently, Bad Religion's "Dissent of Man." I was so ready to hate on that album when I first heard Resist Stance, but when I listened to the whole thing together after it came out, I did a complete 180. I was not prepared for a full recovery like that
Before that, I'd have to say Rammstein's Sehnsucht. Most Rammstein fans tell me that this is their most "popular" (i.e. diluted and uninspired) album, and since it's the only one I own I can't really confirm or deny that, but for what it is, it's not something I'm used to listening to. I was really uncomfortable buying it (got it on recommendation from a friend who lives in Austria), and I was ready for some kind of puke-metal garbage, but when I popped it in, I was pretty surprised --- it's like heavy metal, but with really kickass beats and a crazy synth guy instead of a "lead guitarist." An interesting twist on a diluted genre, IMO.
Before that? Collective Soul started something good with their "Rabbit" S/T album a year or so ago (I heard the first track and thought, "They're back!"), but the rest of that album was kinda meh.
I dunno if it counts as an "album" per se, but the Higurashi/When They Cry soundtrack (by Kenji Kawai) was pretty fuckin' grand. It's so simple yet so creepy. But of course my opinion of it is horribly biased thanks to how atmospheric the show was I still can't listen to the title track without getting Tha Willies.
For all the things that I never did
For all the places I never was
For all the people I never stopped
But there was nothing I could do..."