Monumento Nazionale a Vittorio Emanuele II. And because those aren't enough names, you may also hear it referred to as the wedding cake or the typewriter! It's a gorgeous building - some call it ostentatious - but I've never been here to see the Tomb of the Unknown Solider or go up on the roof to admire the view of Rome.
Roman Forums; other than quickly walking though this area to get elsewhere, again, I've never explored it properly.
The Palace of Justice sits near Castel Sant'Angelo, and it's a beauty of a building. The supreme court of Italy, it requires more than just a passing glance at it, which is all I've ever had time to give it, sadly.