Greyscale and 'tint' textures
A lot of people use greyscale tiling textures and gradients for texturing metal objects, but they're useful for more than that.
If you're looking to lessen lag on a sim or other large area, consider experimenting with prim color. If you make greyscale or tint textures (sepia, cool blue, etc) or a greyscale texture with a bit of color in some spots, you can use prim coloring to give the objects a bit of variety without requiring a lot of textures.
There's a couple items in the Library that use this. Grab a copy of the Sea Fan and see a greyscale texture in action.
To try a tint texture, grab a copy of Seaweed 1 from the same spot and change the prim color on it from green to white. Notice the white one has a bit of yellow on the top and light purple down in the center.
It's also handy with clothing. I've noticed a number of clothing makers that make one or two versions of greyscale textures and tint the various colors instead of uploading each color as it's own texture. I've used this myself, but I found that sometimes it's better to make a light greys version for pastels and a dark version for stronger colors, or to make a warm color version and a cool version.
Torley has a pack of greyscale textures that are fun to experiment with. There's also a couple in here scattered in the other sets.