I'm vacationing in Barcelona for a few days, so I have decided to post a few Spanish scenario ideas.
Homage to Catalonia - The Republicans win the Spanish Civil War...and the Republic promptly fractures. Stalinist, Trotskyist, socialist, anarchist and democratic states populate the Iberian peninsula, bickering among themselves as the Cold War goes on.
The Not-So-Splendid Little War - God (or Cthulhu) himself helps Spain in the Spanish-American War. A freak storm sinks America's Caribbean fleet, with yellow fever killing what forces do land in Cuba. Germany declares war on the US and prevents Dewey from reaching Manila Bay. The entire thing is a farce for the US, and gives Spain enough confidence and indebtedness to Germany to sign some very friendly treaties with Berlin. Spain retains the Caribbean and sells the Philippines to Germany.
Forget the Maine - The USS Maine incident never happens, and neither does the Spanish-American War. The Philippines is eventually sold to Japan after the Hispano-Japanese War, while the US buys Cuba. A richer Spain manages to avoid some of the trouble of the 20th century as a result.
[No name yet] - Spain is victorious over the Dutch in the Eighty Years' War. Dutch Protestants move to England and Cape Colony as the Spanish reinstitute Catholicism with a vengeance. Meanwhile, European power politics continues, especially as religious tensions brew in the Holy Roman Empire.