Larry's answer was thorough and accurate. For a different perspective, here's my take.
Keep it to one page. Brevity and conciseness are key. Some companies may have HR staff willing to look in detail at every resume, but I would guess those are a rarity. I suspect most hiring agents are looking for ways to weed resumes out, rather than looking for reasons to keep you included. You want to say just enough to qualify or over qualify for the job, including any "buzzwords" that the job description lists that you can accurately perform. Yet you don't want to say so much that you risk putting something they don't want, or having it be so detailed they aren't willing to read it through and throw it out for something more "streamlined".
Of course, this depends on the company. Just be honest, be detailed, be concise, and prepare a nice cover letter for any "fluff" that might keep your resume from fitting well on one page.