A quick look at the areas of expertise that create an effective, findable website:

• Designer. These are usually the artists. They handle colors, logos, artwork, backgrounds, template layout. That type of stuff.
• Content/Copywriter. These are the writers. They work with the designer to develop the message and how it’s delivered.
• Developer. These are the tech guys. They worry about how to convert the work the first two guys/gals do to the web. They’re the guys that worry about all those acronyms…  HTML, pHP, Java, MySQL, CMS, WordPress, JOOPLA, etc
• Search Engine Optimization (SEO). These are usually marketing people or tech people with marketing background. They understand what it takes to put your site higher in the search engine returns. They also work with the rest to create content that is useful to search engines.
• Search Engine Marketing (SEM). These are definitely marketing guys. The people managing your Google Adwords account, finding your best fit pay-per-click (PPC) & online advertising.

There are more… the marketing dept that creates your marketing plan, the project manager that pulls it all together and takes you over the finish line…

Depending on your needs, there may be less. Many web pros wear many hats, some focus in one single area.