The Urusov Gambit: ECO C24
An extremely sharp opening for white in chess that usually arises from the Bishop's Opening begins as:
1. e4 e5 2. Bc4 Nf6 3. d4! ...
This opening is named for Prince Sergei Urusov, a Russian aristocrat from the 19th century, who supposedly played it with some regularity. As an interesting sidenote, Urusov played a number of correspondence games with Leo Tolstoy, which are mentioned in surviving letters, but the games themselves have been lost.
This is a very dangerous and sharp line for white, and black must defend carefully. The best refutation of the gambit is probably the so-called Karpov Defense, in which black plays:
3. ... Nc6
Even this solid move leads to very good attacking chances for white, which makes the Urusov Gambit definitely not an opening for the feint of heart.
I have personally found that in amateur play, black will generally accept the gambit. This leads to open lines of play in which white has a strong kingside attack, a lead in development, and the advantange of two tempi gained for a pawn. Not a bad trade at all.
The lack of material surrounding this opening is somewhat disappointing. Gary Lane, in his book Winning With the Bishop's Opening, covers it briefly, and doesn't analyze it very thoroughly. There was also a decent writeup by an amateur player in Holland floating around on the net a few years ago, compiling data he had gathered from myriad sources, but I have since lost my copy and have no idea where to find it now.
I have been using this opening for years, when I get the position, and it is the main reason for my advocacy of the Bishop's Opening.