I know it's a little different, but I'll try combining two civs to make one super civ.
Hunns and Mongols can make a really deadly cavalry force, horses start MADNESS!!!
Austria and Venice, Venice can make the money, Austria spends it on extra CSs to be in your empire, plus Merchant of Venice, nice combo.
Babylon and Korea......HOLY , THIS ONE WOULD BE AWESOME! The early Great Scientist goes great with Korea's UA, and some scientists, along with faster Great Scientists, meaning more Academies, and Korea's UA gives extra science for that.............this would be the most awesome tech civ ever.
Greece and Siam would be the best diplomatic combo ever, it would be unstoppable.
Arabia and Morocco would be masters of the desert and trade.
Byzantium and Celts would be the masters of religion.
Indonesia and Polynesia would be awesome on the Archipelago map.
England and Carthage will become the ultimate seafaring civ.
China and Assyria, free economic-boosting Paper Makers plus China's UA and Chu-Ko-Nu, Assyria's UA plus UB and UU, great way to combine war and science.
Montezuma and Zulu, put Raging Barbarians on, adopt Honor and go for Military Tradition, you are now the ultimate early game millitary WAR MACHINE!!!!
Germany and Ottomans, the free Prize Ships Promotion and Germany's UA will give you a lot of free units, and pay less for unit maintenance for both your navy and your land army-works perfectly well.