I didn't really see any other place to post this, this is about as good as any. Feel free to move it if it's in the wrong location. While these links aren't 100% down to RPG Maker, the color scheme designer and Pictaculous Color Palette Generator may come in handy. The photoshop actions might too I guess....
Obsidian Dawn's Free BrushesWhat it is: Free for non-commercial use brushes for Photoshop and GIMP, the brushes include grunge scratches, and various effects and abstracts, splatters, and even ivy and spider webs.
Color Scheme DesignerWhat it is: A web application that allows you to use a color wheel to generate a palette for use in web design or other uses.
PictaculousWhat it is: Another web application that can even be used on the mobile phone. Upload a GIF, JPEG, or PNG and it will take the base colors and return five of them as color swatches for Photoshop.
50 Time Saving Photoshop ActionsWhat it is: Links to 50 neat photoshop actions, including a pencil effect and a F.E.A.R. "Infection" effect. Worth a look, but most may not exactly be suitable for RMXP/RMVX. The Infection effect might be neat to be used on a tileset though

Enjoy ^_^