Nearly every website can benefit from a few graphics. They draw the eye and brighten up the page; you can also use them to make a point or clarify something you've explained in the text. But for anyone who's not a full-fledged graphic artist or has deep pockets, getting the right images for your site can be a real project.
There are two basic routes you can follow to get images for your site. First, you can grab your digital camera and start shooting. Once you've taken the basic pictures you'll need to tweak them with a graphics editing program; most digital cameras come with software that will help you edit the pictures, but this software will usually only allow basic changes, and its features will often be geared more towards portraits (red-eye reduction tools, for instance). This process requires quite a bit more from you, but if you have the necessary artistic skills you can produce unique, perfectly suited images for your site.
And then there are the rest of us, whose photographic abilities are somewhat lacking. If, like me, you tend to end up with blurry shots of your own thumb, then you'll want to go the other route and use someone else's images for your site. That does NOT mean that you simply download an image you like from someone else's site and post it on your own; that is theft and copyright infringement, and will get you in hot water sooner or later.
Fortunately, there are several cheap or even free sources of images on the web. Microsoft Clip Art is a good place to start, since it's free and you can download as many images as you want – and there are so many images to choose from, you will almost certainly find what you are looking for. The downside is that a lot of small websites use images from the Clip Art database, so there will probably be other sites that already use the same image. A good graphics program and a deft hand with the cropping and shading tools can help give your stock images a new look.
If you're willing to spend a bit, you can turn to one of the many stock photography sites. Some will allow you to buy full rights to their images, meaning that you pay a flat fee and then own the image outright to post as you will. Others use a royalty system, requiring you to make payments for as long as you post the image. The larger sites, like iStockPhoto, offer subscription plans for the serious image-lover, in addition to a la carte purchases.