There's probably no other genre in which long exposures are so heavily used than landscape photography. The convenience of mostly static subjects combined with the necessity of low ISOs means landscape shooters are often pushing their exposures well past the one-minute mark. This interesting video examines three variations on long exposures of similar subjects and how they produce different results.
Coming to you from Adam Karnacz of First Man Photography, this helpful video examines the various ways to take a long exposure shot. I think there's a tendency (at least I know I have it) to simply slap on the standard assortment of polarizing and neutral density filters, which leads to a perfectly fine shot with higher-contrast skies and smooth, glassy water, but it's certainly not the only shot. For example, notice how in the first shot, Karnacz decides to forgo using any filters at all. Instead of smooth water, he ends up with a frothy surface that makes the sea look like fog. Of course, there is really no right or wrong way to go about these types of shots when it comes to such choices; the point is simply to be aware of the various creative possibilities.