Here’s a recipe for today’s wet medium, texture paste, so you can make your own. And it doesn’t have to stay white – try adding some color either mixed in or applied afterwards. The idea is to apply it to a stencil with a flat “tool” & leave a slightly dimensional image behind. Even paint used in this manner (and allowed to dry thoroughly) will work as a dimensional accent! If you don’t happen to own a stencil just punch a few holes through a piece of sturdy cardstock.
For a real treat take a look at Cathy Doerr’s Flickr gallery for lots of ideas for texture & dimension. She takes a lot of classes & posts many examples of the things she has tried, like this gorgeous tag.