Do you mean stuff that is OK for blitz? [fun and ''almost sound''] like Cochran gambit vs Petroff? PLayed it a LOT in blitz.
For fun and fully sound I've played von Hennig-Schara a lot. Both main line and the endgame line. vs Marshall gambit, I occasionally try the g3 line of Fischer's (which is quite rare) and to avoid Marshall completely the early d4 line and doubly delayed exchange. I think both are equal but interesting.
Against Winawer long time ago I played 1. e4 e6 2 d4 d5 3 Nc3 Bb4 4 e5 c5 5. Qg4 Ne7 6. dxc5 . Had some good wins but made the mistake of analyzing it on a computer then lost confidence in it.
That's all I can think of now....
-Bill
ps- I will investigate the4knights idea of yours. It's another way to avoid yet another Marshall!
lets say you want to surprise your opponents with white.
Here are a few ideas I would recommend
1e4 e5
the move Nd5!? will definitely be a surprise for Black
What about 1e4 c5
the idea of 6 Qe2 against the Najdorf is to prepare Be3 or Bg5 and play 0-0-0. Then we play g2-g4. Very dangerous
the French defense 1e4 e6
we give a pawn with white but we will have a furious attack ! what is pawn worth in a bullet, blitz or rapid game ? not much if we are prepared in the line.
what about Black ?
This system, Owen defense is dangerous if White doesn't know it.
and with Black against d4 ?
seems like Black will tranpose in the Nimzo. but on Nf3 we could play f7-f5 then Nf6.
Interesting side line for Black.
what are your favorite lines to surprise your opponent ? and the ones you have the most success in getting them fall into a trap ?