MadShaders is a free collection of 100+ gorgeous pixel shader-based graphics demos, which also doubles as a simple video benchmark tool.
There's a swimming dolphin, flickering jack-o-lantern, Tokyo street scene, fiery star, and a host of other lovingly rendered, ultra-realistic scenes.
Run the program as a benchmark and it displays your frames per second, handy as a basic comparison of graphics speed.
Alternatively, use the option to run all the demos in succession and the program works as a sort-of manually initiated screensaver. Just leave MadShaders running and there will be something new to look at, whenever you glance at the screen.
MadShaders doesn't have the best interface, and if you know where to look then you could find all these shaders (and more) elsewhere. But it does make life easier, there's no installation and it's entirely free, so if you'd like to sample some amazing graphics demos then give the package a try.