"navigation bar" in HTML index?

For the index page that's generated when producing HTML output, is there a
way to get a per-letter "navigation bar" that lets you quickly get to a
particular section of the index?

What I mean is something like this at the top of the index:

[A] [B] [C] ...

where clicking on a letter takes you to the section for the entries
beginning with "A", "B", "C", etc.

Also handy would be either a repetition of the navbar at the beginning of
each section, or a link that takes you back to the top of the page so that
you can click on the main navbar.