I have always liked using "Frozen Charlottes" in my mixed media work - but they're getting harder to find - and more expensive when they are available.
These are the perfect alternative. They're extremely lightweight plastic, so they don't really seem like the real deal until they're glued into a project; then, it's hard to tell the difference.
They tend to be a little too shiny - but some inking takes cares of that - my only complaint (if it's really a complaint) is that they only come in the two sizes. These are the perfect sizes for using in Tim Holtz transfiguation boxes - but a slightly larger size for other uses would be nice.
If you can't get your hands on authentic Frozen Charlotte's these are the next best thing for your altered art projects. With just a bit of work they can be aged to fit into any project. I really like that they come in 2 sizes as well.