Use external USB drives that are self encrypting. You can purchase hard drives that require a code to be entered before it will be accessible. This is a great option if you use external drives for backing up your data or storing any personal information whatsoever. Super easy to use... just don't forget the code!
If you want to encrypt the data inside your desktop or laptop computer, and not lose much in the way of performance, the best way is use SEDs or Self Encrypting Drives. These hard drives handle the encryption at the hardware level so there's no clunky software to install and slow your computer's performance.
You can buy SEDs from your local computer shop and get your favorite tech guy to clone your existing drive to the SED. It may cost you a few hundred bucks but you'll sleep better at night knowing that if your computer is stolen, the data is safe.
The next best option would be a software based encryption like the built-in Windows Bit-Locker (Windows 7 ultimate and above) and fully encrypt your drive. This is a great option for those that don't want to spend money on fancy self encrypting drives but keep in mind it will have more of a performance hit on your system as the encryption is happening on the operating system level instead of on the drive itself.
Finally you can look at third-party software solutions like Symantec EndPoint Encryption which is a centrally managed encryption solution for your entire office. You can encrypt all workstations via a centrally managed console on your server. Pretty slick solution but again, will make a dramatic performance hit on your hardware so make sure your workstations and server are up to the task.
When it comes to securing your data as a whole, there are additional options you can take. Pickup some cable locks and physically secure your computer equipment to your desk. This is a great option if you're using a laptop which is a high theft item. Don't assume that just because it's in your office that it's safe. You may have a cleaning company or contractors that work at your office after hours or you could get broken into.
In conclusion, free buy crypter your data is always the safest route to prevent your business from becoming the next news story but it comes at a cost. Higher performance systems running the latest version of Windows or more expensive self FUD crypter hard drives are required. In the end however it's a small price to pay to make sure your clients confidential data (and your business) is protected no matter what.