What is it called to make my UI pretty?

I'm developing a co开发者_C百科mplex web application. I'm pretty good with the coding and I know about how I want the user interactions to work. My problem is everything I do is seriously ugly. I would like to pay somebody to design the look of the application such as how controls and data are separated, styled and colored.

I feel like what I need is little more than a picture, but I'd definitely be all about some input on the user interactions as well.

What is this called? I was thinking about posting the job on Elance, but I don't even know what to title it.

There is such a thing as Web Site designer, whose job is to only create the graphics and decide what the best way of displaying information and the flow of the site pages is.
Some of them know what they're doing very well that work closely with a coder and already know what the coder wants to accomplish something or their limitation.

They're out there.

EDIT:
Keep in mind, this can be a person that ONLY does a flat Photoshop mock-up of the website, which is then handed to a person to turn it into HTML/CSS, or both those people can be one and the same.

I tend to call it CSS design, HTML layout, or something along those lines.

You want someone knowledgable in HCI - Human Computer Interface

I would call it UI designer (user interface), these designers code in HTML/CSS/JS (all mostly front-end development).

As for the user interaction, you may want to consult a UX designer (user experience).