The most noticeable feature of Piazzale Garibaldi is the huge 19th-century monument to Giuseppe Garibaldi, one of the leaders of the Italian unification movement. In addition to the equestrian statue of Garibaldi himself, busts of other Italian nationals line pathways around the area, along with a particularly striking statue of Anita Garibaldi. Giuseppe's wife, she fought alongside him in South America and Italy (she herself was South American), and this sculpture shows her as I like to think of her - riding a horse and a gun extended into the air in one hand, a baby being cradled in the other.
Another interesting feature of the Piazzale is the puppet shows that are sometimes held there. A Punch and Judy-style stage is always present, and if you're lucky, you might be there on the evening of one of the free shows, enjoying the sunset and the show with the locals.
What brings most people to the Piazzale, however, is its incredible view of the city. Like so many other parts of the city, the Piazzale is on a hill, but unlike other parts, it is not located in the center of Rome, so the view you get is complete. And unlike some of the more popular viewpoints (like the dome of St. Peter's, for example), the hill provides a free and often empty location.