1. Check for broken links on the company site. It's very frustrating for a visitor to click on a link and get an error page. It also sends a message that the company really doesn't think their own site is active or relevant enough to keep fresh. If you don't believe in your own site, why should site visitors.?
2. Archive dated content. Don't take it down. I'm just suggesting that you not have it on the home page under a big banner that says "New". Content that plays high should be timely.
3. Who's on the "About Us" page? If your company has one of those sites that lists the members of its executive team, with bios even; then make sure it's current. I see this all the time; bios of executives who left the company over a year ago and no evidence of their replacement or executives who haven't had their bios updated with their current title. If your director of finance has been promoted to CFO, make sure the web site reflects that. Believe me, your CFO is aware and trying to figure out how to bring it up without looking like an egomaniac.
4. Double check contact information. Has the office moved to a new location? Is the new address on the site? Have the staff members with company e-mail addresses listed on the site moved on? This is probably the most important thing to keep up-to-date. Imagine that really important client lead e-mailing a dead address and moving on to your competitor.
5. Does the look and feel of your company site match other marketing collateral? It should. Is it using the latest version of the company logo and other corporate brands? Is it pushing the same initiatives as corporate brochures and ad campaigns? The corporate web site shouldn't be a year behind the rest of the company, it should be ahead of the curve instead. It may be time for a relaunch.