Though originally made as Cursor Trailers, they can also be used as Floaters and even as clip art if you like. Though mostly transparent, not all of them will look good on dark backgrounds. Some are not suitable for light backgrounds. You'll have to be the judge. The good news is there are a lot here to try.
Click on the image you want to download. Each zipped file contains a set of six images. Then to make them work you need a script added to your Web page. The scripts and instructions for use are on Dynamic Drive: