What a great question! The Etruscans are not a very known people group. The Etruscans were the most powerful and advanced civilization in the peninsula in ancient times. They gave to the Romans many practices. Here are a few things that can be traced backed to the Etruscans.
First, the Etruscans shaped the Romans in terms of religion. They were the ones who examined the entrails of animals. The haruspex (the priests who examined the entrails) were originally Etruscans. This practice lasted well in to the Republic. Second, the Etuscans shaped the Roman form of government. In fact, a few kings of Rome were Etruscans themselves! Finally, the Etruscans helped in the area of architecture. Of course, the Roman improved on this, but the Etruscans started it all off.
As for the early monarchy of Rome, the most important contributions were in the area of religion and mentality to assimilate other people into Rome. This mentality to assimilate people did not die out. In fact, it is probably this fact that allowed Rome to last so long.