8-Bit Textures

Are there any file formats out there that just contain 8-bit texture data? All I want is the width, height, and an array of 8-bit values for each pixel.

http://en.wikipedia.org/wiki/Netpbm_format
http://netpbm.sourceforge.net/doc/ppm.html

You can have an 8-bit grayscale bmp texture.

Does the texture HAVE to support 8-bit only? Or are you looking for a texture format that supports it? If the latter, then just about every texture file format does, even .dds if you create your own without using Microsoft's tools. Have you thought about creating your own proprietary 8-bit texture format?

I'm just looking for a simple image format out there that is used for primarily for 8-bit grayscale textures. Formats like the targa format were good for a while, but I've never seemed to get a fully-supported format working.

I'd recommend .png.
Supports 1/2/3/4 channels at paletted/8/16 bits per channel. Fixed point. Lossless compression using zlib.
The library is relatively stable and there are a few alternative libs available although I've never used them.
Personally I think it wins on bmp/ppm/tga hands down.