The Sloan Digital Sky Survey has imaged nearly a quarter of a million galaxies, the vast majority of them never known to astronomy before. The task of cataloguing them is beyond the capability of current computer technology, and there aren’t enough astronomers to do the job.
Can you help? If you can examine photographs and answer simple questions about them, yes you can. This brief tutorial at the Galaxy Zoo website explains exactly what you need to do. If you need more help, there’s a FAQ, a forum and a blog, and they’re on twitter.