Cayo, as San Ignacio is referred to by the locals, is a great little town. If you've come to the country by way of Belize City, this place is completely different. A pictureqsue location, laid-back atmosphere, and very friendly people.
Cayo is a great place to spend a few days, as it makes a wonderful base to visit incredible sites in Belize such as ATM Cave (Actun Tunichil Muknal), Xunantunich and Caracol, and Cahal Pech which is on top of the hill in San Ignacio. On top of that, there's the advantage of being so close to the Guatemalan border, that a day trip to one of the most impressive Mayan sites in the world, Tikal, is a must.
Burns Avenue, the main street in town, is lined with quaint guesthouses, lively bars, good restaurants, and tour companies which can arrange tours to any attraction in the area.