has a pretty good rundown of the Saxe-Coburg dynasty.
The Ducal House provided monarchs and consorts to:
Duchy of Saxe-Coburg and Gotha
(formerly the Duchy of Saxe-Coburg-Saalfeld until it was renamed in 1826) Reigning Dukes until 1918.
In 1893 Queen Victoria's 2nd son Prince Alfred, Duke of Edinburgh, became the Reigning Duke of Saxe-Coburg and Gotha.
On the death of Duke Alfred in 1900 the Dukedom passed to Prince Charles Edward, son of Queen Victoria's haemophiliac son Leopold, Duke of Albany. As Karl Eduard he was the last Reigning Duke of Sace-Coburg and Gotha.
: Princess Sibylla, daughter of Karl Eduard, married Crown Prince Gustav Adolf in 1932. Their son reigns today as the King of Sweden.
S-C & G connections:
: Princess Marie of Edinburgh (and from 1893 of Saxe-Coburg and Gotha) became Queen of Romania in 1914 as consort to King Ferdinand I. He was the son of the Prince of Hohenzollern (-Sigmaringen) and the Portuguese Saxe-Coburg Infanta Antonia.
Hesse and by Rhine
: In 1894 Marie's sister Princess Victoria Melita married Ernst Ludwig, the last Grand Duke of Hesse and by Rhine (aka Hesse-Darmstadt). They were divorced in 1901.
: The now-divorced Princess Victoria Melita married Grand Duke Kirill of Russia in 1905; he proclaimed himself Head of the Imperial House of Romanov and Curator of the Throne in 1922 and Emperor and Autocrat of all the Russias in 1924; their son Grand Duke Vladimir became Head of the Imperial House of Russia in 1938.
: In 1938 Victoria Melita and Kirill's daughter Grand Duchess Kira married Prince Louis Ferdinand; he became Prince of Prussia and Head of the Royal House of Prussia in 1951.
: In 1898 Princess Dorothea of Saxe-Coburg and Gotha was married (or sacrificed) to Ernst Gunther, Reigning Duke of Schleswig-Holstein. Queen Victoria referred to him as "odious Gunther" and unsurprisingly there were no children of the marriage.
Princess Victoria of Saxe-Coburg-Saalfeld married Prince Edward, Duke of Kent in 1818; their only child became Queen Victoria;
Prince Albert of Saxe-Coburg and Gotha married Queen Victoria in 1840; from 1901 to 1910 King Edward VII was the first British Saxe-Coburg monarch; George V was a Saxe-Coburg until 1917 when the House and family name was changed to Windsor (it was quickly applied retrospectively to 1910).
: Victoria and Albert's eldest daughter Victoria married Prince Friedrich of Prussia and in 1888 became German Empress and Queen of Prussia. Mother of the Kaiser.
Hesse and by Rhine
: V & A's 2nd daughter Alice married Hereditary Grand Duke Ludwig and in 1877 became Grand Duchess of Hesse and by Rhine.
: Princess Margaret, daughter of Victoria and Albert's third son Arthur, Duke of Connaught and Strathearn, married in 1905 as his first wife Gustaf Adolf, Crown Prince of Sweden (later King Gustaf VI Adolf). She was the mother of Prince Gustaf Adolf (the current King of Sweden's father) and of Queen Ingrid (the current Queen of Denmark's mother).
: In 1896 Princess Maud, the youngest daughter of Edward VII, Britain's first and last Saxe-Coburg King, married Prince Carl of Denmark. In 1905 he was elected King of Norway and she became a Queen.
Prince Leopold of Saxe-Coburg-Saalfeld, formerly married to the tragic Princess Charlotte of Wales, only child of the Prince Regent, later King George IV of Great Britain, became the first King of the Belgians in 1831 and established a new branch of the dynasty. The House name remained Saxe-Coburg and Gotha until it was dropped during the First World War.
: Leopold I's daughter Princess Charlotte married in 1857 Archduke Maximilian of Austria. He became the short-lived and soon-executed Emperor of Mexico while she became the long-lived and quite mad Empress Carlota.
: Leopold II's daughter Princess Stephanie married the ill-fated Rudolf, Crown Prince of Austria in 1881. He committed suicide with his mistress eight years later.
: Stephanie's younger sister Princess Clementine married Prince Victor Napoleon, Head of the Imperial House of Bonaparte in 1910.
: Albert I's daughter Marie-Jose married Crown Prince Umberto in 1930 and became Italy's last Queen.
: Leopold III's daughter Josephine Charlotte married Hereditary Grand Duke Jean in 1953 and as his consort later became the Grand Duchess of Luxembourg.
(the Catholic Kohary branch of the Saxe-Coburg & Gothas)
Prince Ferdinand of Saxe-Coburg and Gotha married Maria II da Gloria, Queen of Portugal and the Algarves in 1836 and was created King Consort of Portugal as Fernando II in 1837; their son Pedro V became King in 1853; the dynasty reigned until 1910.
Maria and Fernando had two daughters, the Infantas Maria Ana and Antonia:
: Maria Ana married Georg I, King of Saxony in 1859. Their daughter Maria Josepha married Archduke Otto of Austria and was the mother of Karl, the last Emperor of Austria and King of Hungary.
: Antonia married Leopold, Reigning Prince of Hohenzollern (-Sigmaringen) in 1861. Their son Ferdinand became King of Romania.
Prince Ferdinand of Saxe-Coburg and Gotha ("Foxy Ferdinand") was elected Prince of Bulgaria in 1887 and became Tsar (King) of the Bulgarians in 1908; the dynasty reigned until 1946. The last King, Simeon II, was elected Prime Minister of Bulgaria in 2001.