Various background effects can be included to the application design ranging from the simple three point gradient white backgrounds to the fancier picture backgrounds that make the ideal backdrops for fluidic web designs. Most backgrounds can be simply obtained as editable PSDs and can be layered on to the design with simple editing options, saving the hassle for the designer.
Selecting the right background depends on the nature of content that will be portrayed on it. Also the style of the base theme used will also influence the selection of the background. For instance textures are ideal for mobile applications that have a lot of text content to display whereas picture backgrounds will be more appropriate for travel and tourism based web designs. But nevertheless the sources to choose the backgrounds from are plenty. Here is a compilation of the best resources where you can find high quality background styles including various patterns and wallpaper styled backgrounds with ease.