Taglibs, or rather the custom tags within a tag library, and JavaBeans are both technologies for wrapping up common functionality as reusable components. Whereas JavaBeans can be used in JSP, Servlets and simple applications, custom tags are a part of the JSP specification and therefore can only be used with JSP. Essentially, JavaBeans can be reused anywhere that there is
Java, while custom tags need to run inside a JSP container.
For a more detailed comparison, including examples of what you might want to use each for, check out
Chapter 8 : Tag Patterns (from Professional JSP Tag Libraries) that is free to download in PDF format.
Hope that helps
Simon