People often associate long exposures (or long shutter speeds) with night photography. But there are amazing photos you can get with longer shutter speeds, ranging from 1/15 of a second up to hours. They don't require sophisticated cameras and lenses.
The challenge for obtaining long exposures in the daytime is how to reduce the amount of bright daylight to allow for a longer exposure. Stopping down your aperture won't be enough, because you need to block a lot of light. The solution is to use a Neutral Density filter. These filters are tinted with a "neutral" color, serving no other purpose than to reduce the total amount of light into the camera. ND Filters come in many configurations, from one stop of light, up to thirteen stops, where each "stop" doubles the amount of time of your exposure because it blocks twice as much light as the previous stop.
I usually carry with me a 3-stop and a 10-stop ND filter. And that's where the fun begins for things like waterfalls, fog and just normal street scences. Like this picture shot in Hong Kong. As some photographers do it I tried to do three different images at 8, 9 and 10 minutes, put them together in CS5 - HDR and tonemapped them. At last put a monochrome tint on it.