Assuming you have basic HTML/CSS skills, you can find everything you need on the web available at no cost to design a nice looking, professional website.

First we will start with some web design tutorials.

Next you need a grid system to hold up your site structure. Try the 960 Grid. Very good, very free.

960 Grid

Then you need a color palate. For the best custom color palates that always look good, use the Color Scheme Designer.

Color Scheme Designer

Now some graphics. Now that you have an awesome color theme, find some graphics to match. Some free stock photo resources are listed here.

Maybe you want a drop down menu. Try the suckerfish family. It has been built on and improved so many times, you should easily find something suitable. Here is a link to Son of Suckerfish.

How about some cute icons? RSS, twitter birds, download, etc. can all be found by the hundreds from any graphic or web designer that is trying to get web traffic. Smashing Magazine has a post with some really high quality free icons. Here is another good resource for free icons.

Free Icons

If your graphics and icons are looking a little clunky next to each other, you can edit them with Gimp.  Gimp is a free image editing program along the lines of Photoshop.

Gimp

At this point, you have everything you need to be able to put together a reasonable looking, valid xhtml/css-based website.

W3C Validation Service