userstyles.org - Rantzien

This style makes the stream slightly more compact and reduces its font-size, but what made me want to share it is the neat image handling. The huge images in the stream are scaled down to a thumbnail, and when you hover over one, it smoothly scales up to size. The last part requires a modern enough browser to handle CSS animations, of course.

mail.com is a pretty good webmail service but their login page is terrible if you're just trying to login to your email. This style obliterates everything unnecessary on it.