I'd like to suggest that you "keep it simple" and do only three things with the goal of retaining your employees. If you do, you'll go a long way towards keeping those precious assets at your company.
1. Have a Competitive Benefits Package
If your product or technology is state-of-the-art, but your benefits package hasn't been updated in the past few years, you had best change that. If you think that your benefits package is a "gift" to your employees, rethink that. We get calls all the time from disgruntled employees looking to make a job change. Many times their meager benefits package is just what pushes them over the edge to start a job search. For example, three weeks' vacation from the start of employment is now just about standard issue.
Your benefits package should not only be a great recruiting tool, it should be so robust that it delights your employees and keeps competitors from stealing your people. And, there are many benefits that don't actually cost a lot of money but will get you lots of loyalty in return.
I recommend: Cutting Edge Technology - Retro Employee Benefits
2. Compensate Your Employees at Market Value
When you hire a new employee, the market will pretty much determine what compensation you'll have to pay. But what about the employee who has been with you for a long time? Do you know if his compensation is competitive with the market? In many cases, an employee's job may have changed since he has been hired. Maybe he has taken on more responsibility, or maybe he has a long tenure with you. Whatever the reason, if you find out the compensation is not competitive, you had best change that immediately. One of the most frequent comments we hear when someone starts a job search is that they feel they are "not making what I'm worth." And, sadly, many times they are right!
I recommend: Salary.com
3. Just Say "Thank You"
There are no words you can say that are more important than simply saying "Thank You" when a job has been well done. People leave their jobs when they think that what they do is not important to the company, when they feel they are not valued and appreciated. And, people who are making competitive salaries will still leave their jobs when they don't feel appreciated.
Thank your employees often - in private and in public. Be sincere in your appreciation and in your words. If this "isn't your style" or you feel awkward saying these words, practice in the mirror until you feel comfortable. Change your style. Do whatever you have to do to communicate your appreciation. As the Nike ad says, "Just Do It!"
I recommend: Ongoing and Informal Ways to Say Thank You