There is nothing that looks worse than a crooked horizon line. It's like when you don't get the fleshtone color right in a photoit just jumps out at people (and people can't resist pointing this out. It doesn't matter if you've taken a photo with composition that would make Ansel Adams proud, they'll immediately say, "Your photo's crooked"). A great way to avoid this is with a double levela simple little gizmo that slides into your flash hot shoe (that little bracket on the top of your camera where you'd attach an external flash). This double level gizmo has a mini-version of the bubble level you'd find at Home Depot and it lets you clearly see, in an instant, if your camera is level (and thus, your horizon line). The double level version works whether your camera is shooting in portrait or landscape orientation and is worth its weight in gold (of course, that's not saying very much, because I doubt the thing weighs even one ounce, but you get my drift). As luck would have it, they're more expensive than they should bebetween $25 and $75but still very worth it.
