Gloobus is an extension of Gnome designed to enable a full screen preview of any kind of file. Globus currently supports the following files: TXT , PDF, JPG, BMP, GIF, PNG, PSD, MP3, OGG, MPG, WMV, XCF. Finally I can preview PSD and XCF files :D. Using Globus is very simple. Just select the file in Nautilus and hit the key. Before you get started with installing Globus, please take a look at the following 2 screencasts with Globus in action (I know you will most definetly want to install Globus after watching those...):