After searching for wedding photographers today I've come up with a list of shall and shall-nots for wedding photographer web sites (many of these can apply to any type of photography).
First: don't use Adobe Flash (as opposed to flash photography, which I'm all for). I know Flash allows you to position things just so with cool effects in a way that HTML and CSS do not, but its negatives are too high. The Flash plugin has to be installed in the browser. Script blocking like NoScript means your site will have to be unblocked. Flash takes more time to load than an HTML page. Each one of these is a barrier to potential customers. If you think you need Flash to get your message across effectively, then rethink your message.
Don't use slideshows, Flash or otherwise, to show your work. You or a web designer can spend a lot of time trying to get the perfect timing to synchronize pictures with music or displaying a picture on-screen for just the right length of time so that a viewer can appreciate your talent. But after all that effort your judgement will almost always be wrong. I didn't want to sit through a slideshow at the rate that the photographer wanted, I wanted to go faster (or sometimes slower) but on some sites the automatic slide show was the only choice. I had problems with slideshows that had previous or next buttons, often the controls responded sluggishly and in a few they had no effect at all. Also, there is no reason to ever play music. I was already listening to my own audio thank you very much before your renaissance guitar muzak started. It's infinitely worse when there is no way to mute it! I became frustrated and left such sites quickly.
You shall not watermark your pictures in any way. I know there is a lot of fear about pictures being stolen, but a watermark is distracting and often ruins the photograph. Do you want potential customers to notice your watermark, or your work?
Don't have a lot of text. You're a photographer right? If text takes up more space on a page than photographs then it's wrong.
Do tell a story with your photographs. In fact tell your story by telling your customers' stories. Your potential customers visiting your website don't care how you feel about their special day and how you are gonna work really hard because you believe in the power of love. They want to see your style, even more they want to look at your pictures and imagine themselves in them. What you choose to show should allow viewers to do that without distraction.
Allow customers to see your work quickly. Don't worry about elaborate slideshows with thumbnail navigation and music; don't even do single picture Flickr-like viewing. Allow your customers to see a group of pictures that tell a story on one page. Some photographers allow you to choose from a list of weddings and then a set of pictures from that wedding are displayed on a page. No waiting for Flash or clicking clunky navigation buttons; scrolling allows all the pictures to be seen at the viewer's pace.
Know what your customer's are buying, not what you are selling. A photographer probably wants to sell prints, photobooks, or DVDs so that they can eat. But I believe the reason customers go to a photographer's website is to see if they like the style (at least that's what I was doing). The first thing a customer should see is your pictures, not the products they can make with them. Things like products and pricing and "about" pages should be available but if potential customers like your work, they'll be willing to spend some time (probably a second or less) hunting for them on a menu.
So the advice to photographers (of all kinds) from an amateur about what your website should look like is: make your photographs easily viewable, tell a story with your photographs, and don't distract from the story. As an example Paul Rowland Photography is the most effective website I saw today. It's not perfect, the home page features Flash loading, but the list of couples' names under Weddings leads to blog-like pages where the photographs are the main focus, they are easy to view at my pace and they tell a story that any potential bride could imagine herself in.