i'm teaching a course on 'american political thought' and i've been reading pretty hard in the founders. i've drawn the conclusion (not that many haven't drawn it before me) that john adams was, by a ways, the best, the most formidable, the most knowledgeable, the most scholarly, the sharpest-edged intellect among the founders. one extremely neglected just virtuoso moment is a defence of the constitutions of government of the united states of america (it's a defense of the state constitutions (including his own constitution for massachusetts), written before the national constitution was ratified). it's a three-volume response to a three-page letter from the french thinker/statesman turgot that constitutes an exhaustive history of republican ideas. he's got all the roman historians, machiavelli, harrington, locke, montesquieu, and many others all in their original languages. he's got the swiss cantons, the italian city-states, the dutch republics, an exhaustive sense of english political history, and then there are the incas, zoroaster, india etc etc: an absolutely exhaustive history of republican ideas.
no other founder could have done this; none could even have assayed it. jefferson was a formidable intellect, but by comparison a dilettante. franklin was delightful and sharp as a tack, but not a scholar on this level. it's an intimidating book - though adams can be quite a delightful writer - but still it deserves a lot better than it has gotten; it's out of print, and has rarely even been issued as a book; people who read it usually read it as part of the complete works. well i daresay it needs a revival and a new scholarly edition. but that itself is a vast and intimidating project.
and adams' thought is the most influential on the shape of the american constitution, though all these guys were separation of powers type republicans of one sort of another. and i love his marriage best of all: he loved the fact that abby kicked ass.
update: well i guess it's not out of print if you're ready to drop $250. geez.