The Budapest Gambit (1.d4 Nf6 2.c4 e5!?) is a swashbuckling gambit where Black assumes the initiative from the word go and will most often recover his pawn with a well developed game.
FOXY OPENINGS - VOLUME 15 - Budapest Gambit
In part 2 of the series IM Valeri Lilov examines a sharp repertoire for both black and white. A complete system you can employ in your own games! Valeri's take on theory is both aggressive and based on sound strategic principles. He examines White e 4 and one good line of play for all of Black's possible responses with the Budapest Gambit. Also, how White can respond to the Budapest Gambit and how to respond to deviations on most of the various openings including with the Grand Prix attack.
An Opening Repertoire for the Attacking Player Lectures 5-9 - Chess Lecture - Volume 81