love for sale is his best work, some of the live versions of cuts on airtight's revenge were ridiculous (look up the vtech / cmj performance of levels from 2009). a love surreal had some dopeness too (right at the core, astray, slipping away, never be the same). some standout tracks from the first album were love poems, queen of sanity, sometimes, home, when will you call, reminisce...
as far as joints he's covered...led zepplin's since i've been loving you, bob marley's is this love, soft cell's tainted love. i like the joints he's done with robert glasper recently too (all matter, always shine, letter to hermione which was a david bowie cover), he really shines as a jazz singer