Civil engineering is arguably the most long-standing of the engineering disciplines. I've been told that the name dates back to when they needed to make a distinction between military work and civilian work, but I don't have a citation for that.
You can't go a single day without relying on something done by a civil engineer. Roads, bridges, water supply, sewerage, shopping centres/office towers - they all fall under the civil umbrella. Even planning the sequence on the traffic lights to keep the traffic moving smoothly is usually a civil task.
Environmental engineering is a growing sub-set of civil engineering. As the name suggests, they usually deal with things like environmental impact statements and water quality.
Civil engineers do some pretty spectacular things, like the Milau Viaduct in Spain (featured in Richard Hammond's Engineering Connections, which just by the way is a fantastic show, even if you're not an engineer).
Of course, they're human and they don't always get things right... Footage of the Tacoma Narrows bridge collapse in 1940 is something that almost every first year engineering student sees.
Tomorrow, mechanical engineering.