If you're an entry level candidate less is more and a page should be plenty. For more experienced candidates it's fine to have a longer resume.
Resume Length Tips
Here are tips on how to decide on resume length from David Adams, Vice President of Learning and Development of Adecco Group North America:
How long is too long? The length of your resume should be based on your experience and the type of job you're seeking. Some general guidelines are:
Less is more for entry level applicants. Entry level job seekers or those transitioning between career fields should stick to a one page resume.
Other times, a little extra is OK. or mid-level candidates with around five to ten years of experience or anyone whose field requires technical or engineering skills, a two-page resume is common. It allows enough space to include all of the pertinent information in a readable manner. The key is to fill all, or at least three-quarters, of the second page with relevant and helpful information so that recruiter's attention is not drawn to the blank space on the second page.
Senior executives can write away. Executives or senior-level managers with a long list of accomplishments in their field - or those in an academic or scientific field whose experience includes a number of publications, licenses or patents - are the only people who should be circulating a resume that is three pages or longer. When a multiple-page resume is appropriate, an addendum can be used after page two. This allows job seekers the option of including the full document depending on the requirements of the job.