With new monitors available, screen resolution for users is increasing, leaving lots of un-used space on web pages. Web pages that stick to older resolutions can be unsightly. All that wasted space!
Filling the page with content isn't always the way to go either. Reading clear across the screen can be difficult. Content should be kept in easy to read chunks. Use fixed width table cells or CSS width tags to keep a column of text narrow enough for the reader to easily scan and read the text.
So, what design techniques will give that page a finished look? Use design elements like banners and side bars that reach across and down the page. Make your viewer feel good about their fancy screen. A touch of color or design can fill that space, saying that you have thought about how to use it, and leave a "finished" feel with the users.