FSAA Full Scene AntiAliasing. Increases image quality by removing jaggies at the edges on polygons. It does this by supersampling, that is, it renders to higher resolution offscreen surface, and then downscales it. FSAA is very expensive and is thus recommended to be turned off or set to a lower supersampling ratio such as 2x. If you monitor supports higher resolution it's recommended to use it insteed of FSAA in a lower resolution.

Subpixel precision Sets the subpixel precision value, higher gives better image quality. There's no performance hit as I know and it is thus recommended to be set to highest possible.

Max anisotrophy Sets the level of anisotrophy that will be used if application doesn't set it itself (very few does). The level of anisotrophy denotes the max ratio between the lengths of the sides of the sampling window. In other word, when a polygon is viewed in a steep angle it will take more samples along the direction of the perspective. Radeon supports a anisotrophy of 16 which means it can take up to 32 samples along the direction of the perspective and 2 in the other direction at most. Anisotropic filtering enhances the image quality by reducing the blurriness that occures on those steep angle viewed polygons and will give a generally sharper image. However, it's a not for free, so setting it high may make you lose some performance. Turning it off completely is recommended.

LODBias Set the Level Of Detail Bias. That is, setting a higher value will make it take samples from higher order mipmap levels earlier. High LOD Bias means more detail and higher image quality. High LOD Bias comes with a small performance hit. Recommended settings are 5 or above.

Depth/Stencil Sets the available bitdepths for the depth buffer (Z-buffer or W-buffer) and the stencil buffer. Forcing 16bit depth buffer may bring a few fps in some games. If the card is short of memory this can be a very good tweak to get a lot of extra fps. When playing texture intensive games such as Unreal Tournament on a 32MB card I recommend forcing 16bit Zbuffer. It'll save you a couple of megs of video RAM and thus reduce the AGP texture swapping (which is a major fps killer). For other applications I recommend setting the 24/24+8/32 mode. Some applications that require a Stencilbuffer may either not run or will run with some effects disabled (such as water reflections etc).

Dither when alpha-blending This sets how dithering should be done if it should be used at all. This setting only applies to 16bit since no dithering occures at all in 32bit. Enabling dithering improves the experienced color range, however it may introduces annoying dithering patterns. Error diffusion dithering generally produces better results than ordered dithering. Disabling dithering will remove the ditherings patterns but will on the other hand give more banding. There's no performance difference between the settings, so choose what you think looks best. My choise is error diffusion dithering.