Robert Christgau is an American rock critic, best known for his letter-graded capsule reviews, for being one of the earliest rock critics (and the oldest one currently working), and for being one of the first mainstream reviewers to cover hip hop, punk, and African imports. His style and taste are incredibly divisive, but also adventurous, smart, and endlessly fun - I've found ridiculous amounts of great music through him.
His website defines an A+ album as "a record of sustained beauty, power, insight, groove, and/or googlefritz that has invited and repaid repeated listenings in the daily life of someone with 500 other CDs to get to."
The list was taken from the A+ list on his website, plus the 50 albums on his ballot for Rolling Stone's 500 Greatest Albums list. There are also numerous ungraded/unreviewed albums he's stated are A+ on his Xgau Sez column. Finally, there's several A+ albums he downgraded in retrospect (Neon Bible, etc).
In short, it's as complete as I could get.....