If you take photos in RAW, would it be nice to insert the SD card into your PC and be able to view them immediately without converting them in Lightroom first?
For Windows 8 and 8.1, just download the Camera Codec Pack from Microsoft download center. Install it and reboot. Then you can view thumbnails in Explorer and double click to view them in full size. You may do some simple editing and save a copy in jpeg, very convenient.
For Windows 7 and earlier versions of Windows, you need to install FastPictureViewer Pro (free). For this purpose, you may select only the basic program and the RAW codec for your camera during the installation process.