I ran across this quote on the homepage of a photographer's business site:
Spalding Media Services specializes in all forms of photography.
From a marketing standpoint, there's a problem with that. If I'm looking to hire a freelance photographer for a certain project, I want someone who specializes in that particular thing. I don't want a commercial product photographer shooting my wedding day. On the other hand, I don't want a child photographer taking the photo I'll be blowing up to put on a billboard along the freeway.
A general approach -- "I specialize in everything" -- is what you want if you're looking for a job with a company that might reasonably have a broad range of needs. The general approach emphasizes versatility and flexibility, not strength in a particular area. That statement only means "I don't specialize in whatever you're looking for."
If you're looking to sell yourself to clients for specific projects, you need to match those specific projects as well as possible. "But how?" you ask.
The Internet makes it possible. (That should be read in a dramatic, commercial voice-over tone.)
Pick the areas that you really do specialize in. Develop them as subdomains -- weddings.photographername.com. Each subdomain should be a tightly focused site with your strongest examples of that type of work and clear calls to action -- a "contact me" form, or a link to your contact and pricing page. That pricing page should be specific to the subdomain. So somebody who's looking for wedding photos shouldn't see a page that lists your prices for studio shots.
Your main site can carry the general pitch, but only if you're also looking for a job. Otherwise, you should pick your profitable niche and focus most of the main site on that. The main site is also where you could throw in a relevant blog or other content.
If you feel you must cross market -- because maybe the people who are getting married also restore and custom detail Harley Davidsons -- keep it subtle. If they really want to see your other stuff, they'll find it through a link in the main site navigation.
If you're reasonably creative, you can see how these principles would apply to many other situations. If you're not that creative, and you have bags of money, you can hire me to come apply them (and countless other marketing and technology ideas!) to your particular situation. :o)