Banner Ad is cut off

The width of your sidebar is only 240px. The banner extends a bit wider than that but then is cut when it reaches the extent of the page wrapper:

I would suggest using a different banner because 300px is just too wide for your sidebar and will look odd if it’s actually that wide.

Otherwise if you don’t mind making your sidebar wider and the whole site wider you can change the widths as shown below:

#page .wrapper {
    background: url("images/wrapper_bg.png") repeat-x scroll 0 0 #F5F5F5;
    margin: 0 auto;
    position: relative;
    width: 1060px;
}

#secondary {
    float: right;
    margin: 10px 20px 0 0;
    width: 300px;
}

However you will then have to fix other style elements also to make them wider to match, such as nav bar etc.

You can use a tool such as Firebug to help in making style changes to you site.