Difficult decision, indeed. Several answers.
Streetlight Manifesto - Everything Goes NumbA nifty entry into the ska-punk genre, combining genuinely interesting composition with lyrical stylings typically not seen outside of hardcore punk (albeit slightly more decipherable and less grating than most vocals in that genre). The lyrics also definitely spark the imagination once deciphered, and are riddled with mature takes on self-identity and uncertainty. That, and it sounds fucking awesome.
Frank Zappa - Apostrophe (')Zappa and the musicians he worked with on this album were in top form here, boasting his genuine weirdness mixed in with satire and societal commentary while being inventive and impressive, musically. This record got me into Zappa, and continues to be the one I listen to the most.
They Might Be Giants - John HenryThe first time TMBG utilized a full band, and this album shows some of their less peppy songs (despite the keys they might be written in to throw off the listener), and the lyrics are quite clever and intriguing to analyze. It was fun to hear the difference the added instrumentation made in how much they have access to (especially looking at how it's shaped their modern style), and it's all thanks to this lovely piece of work.
Runner-ups:- Clap Your Hands Say Yeah - Clap Your Hands Say Yeah
- Honeyhoney - First Rodeo
- Diablo Swing Orchestra - Butcher's Ballroom
- The New Pornographers - Challengers
- Rasputina - How We Quit the Forest
- school food punishment - amp-reflection
- Ingrid Michaelson - Everybody