What video modes does my card support?

Using fbset, you can program video modes (see the framebuffer documentation in the kernel tree for details). However, there are some modes built into most drivers that you can specify at boot time: typical mode names are 640x480, 800x600 and 1024x768. Some cards can also autodetect the mode you enable in AmigaOS and use it.

As of kernel 2.1.124, here is a fairly comprehensive list of supported modes. "bpp" stands for "bits per pixel": it is the color depth. All modes are non-interlaced unless otherwise specified.