USGS has just released a Fact Sheet providing information about their LandsatLook images. LandsatLook images are full resolution JPEG files derived from Landsat Level 1 data products. The images are compressed and stretched to create an image optimized for image selection and visual interpretation.

If you want step-by-step instructions on how to download LandsatLook images, follow these instructions.
Further Information:
+ LandsatLook Images 
+ Get a LandsatLook Image, step-by-step instructions (PDF)