The Suburbs (2010)
This may be the Arcade Fire's best album yet, and it's definitely their most accessible, not to mention commercially and critically successful. If you're new to Arcade Fire, you might want to start here and work backwards.
Funeral (2004)
This darker, stranger album from Arcade Fire's earlier days is clearly concerned with many of the same themes as The Suburbs: place, community, geography, and death loom large (hence the title). The die-hard Arcade Fire fan will probably like Funeral the best.
Neon Bible (2007)
To needlessly employ a double negative, the Arcade Fire is never not apocalyptic. You'll know what we mean when you hear this album.