PSD files are used by Photoshop Elements and Photoshop and is the main format we will be using.
Photoshop Document file. PSD files retain layers and can be edited later.
Photoshop Document PSD file stores an image with support for most imaging options available in Photoshop. These include layers with masks, color spaces, ICC profiles, CMYK Mode (used for commercial printing), transparency, text, alpha channels and spot colors, clipping paths, and duotone settings. This is in contrast to many other file formats (e.g. .EPS or .GIF) that restrict content to provide streamlined, predictable functionality (read more at Wikipedia).
I personally recommend using PSD to save your scrapbook pages, as they will not lose any features that may not be supported in other formats, such as TIFF.