Irfanview is a professional, free program for viewing a wide range of image types. Irfanview is also very capable of manipulating images using tools such as sharpen, blur and can resize and
resample images.

Irfanview can import a variety of file formats from JPEG, GIF and TIFF files as well as Adobe'Photoshop (PSD) format 

Images can also be saved to many different file formats such as JPEG and GIF as well as saving as a Macromedia Flash file.

There are also useful tools such as batch conversions which makes life easy if you need to work with a lot of images, for example resizing thumbnails for a website. Other useful things include getting exif information from digital cameras. 

Irfanview is a great tool if you want to get some image work done quickly as it is a light weight application. If you are a designer or work with images often you need this free software.