Here is the first example that springs to mind: in 1167, most of the cities of Northern Italy formed an alliance called the Lombard League. The League was supported by the Pope and defeated the Holy Roman Emperor Frederick I. (Here, one could make an analogy with the Delian League defeating the Persian empire). As a result, Italian towns gained considerable independence from the Empire and gradually evolved into the city-states of the Renaissance period. After defeating Frederick, the Italian city-states saw no need for maintaining the alliance, which was therefore dissolved, but there is no denying that they were culturally-linked and that they collectively ended up having a huge impact on human civilization.
As to Alexanders empire, it was, strictly speaking, more a Macedonian Empire than a unified Greek state. Its successor states, such the Ptolemaic and Seleucid empires, may have had great importance... but to consider them as the legacy of some sort of Greek national unification is, in my opinion, stretching things a bit too far. Its more correct to say that mainland Greece was conquered by Macedonia, but kept having a strong cultural influence (which it retained even after the Roman conquest).
As to the Italian UU: "Condottieri" were the mercenary's leaders, so I think that the term is more appropriate for some special type of great general. The UU could be "compagnie di ventura", which were the mercenary bands led by the condottieri.