The purpose of helpers is not, as others here imply, to help developers who don't know how to write HTML. The purpose is to encapsulate common functionality -- so you don't need to write the same thing a thousand times -- and to provide a single place to edit common HTML used throughout your app.
It's the same reason templates and SSI are useful -- not because people don't know how to write the HTML in their headers and footers, but sometimes you want to write it just once.
EG. What happens if/when HTML 5 is
finally implemented and Django is
generating HTML 4 or XHTML markup?
Same thing that happens when HTML 5 is implemented and all your templates are written in repetitive HTML, except a lot easier.
The other posts have already answered the question, linking to the docs on custom template tags; you can use tags and filters to build your own, but no, there aren't any built in.