Rav Chaim David Halevi comes to mind in terms of his Piskei Halacha related to saying Nachem in 9 Av after the Six Day War and on the Halachot of redeeming Israeli soldiers held in captivity.
Rav Unterman's Psak related to Police work on Shabbat in The State of Israel is another example.
More on all of these at another time.
For now, I want to call your attention to an amazing psak from Rabbi Shlomo Goren.
Follow this link to learn how the Establishment of the State of Israel
|Rabbi Shlomo Goren|
Seeing Halacha this way is one of the clearest ways to show that Halacha is a living entity and that it can respond to changing historical circumstances.