Sort posts by title on the archive

Hi I hope someone can help.

I am looking for a way to put filters boxes dropdowns or otherwise on the front end of my website so that when a reader is viewing a category they can choose to sort by title a-z or by tag a-z etc.

I have found out how to sort a category a-z by adding a function but it would be really useful if there was a way of readers being able to do this on the actual website.

Anyway ideas?