Sound gambit against e4

Im looking for a sound gambit against e4.I have yet to find one besides the elephant and lativan which are unsound.Are there any sound gambits or most I play a classical opening if so whats the most aggressive choice.

e4..e5     Nf3..Nc6      Bb5...f5

e4...e5   Nf3...Nc6    Bc4...Nf6    Ng5..d5     exd5....Na5

these are both very playable

I hesitate to call Schliemann (3...f5!?) a gambit since the main lines have White replying 4. Nc3 or 4. d3.

Other than 5...Na5 in the Three Knights (after 5. exd5), the Ulvestad (5...b5 6. Bf1 Nd4) is worth considering, or Fritz (5...Nd4) which often transposes to the 5...b5 line.

Though if you're looking for responses to 1. e4 in general, as a materialist I don't think Black is in a great position to spring gambits everywhere. ;)

It's possible to play 1. e4 e5 2. Bc4 f5. 

Or 1. e4 d5 2. exd Nf6 is okay for black if the game continues 3. c4 c6.

The problem with Black countergambits in open games is that White is already half a move ahead in development and that makes it difficult to make a gambit pay off for the second player. Ideally, you want to play a gambit to throw your opponent off balance and sieze the initiative, not just lose a pawn and damage your position.

That being said, the two most promising efforts are the Marshall Gambit vs the Ruy and the various Two Knights Defenses after 4.Ng5