This extension for Magento saves the customer's currency selection not only in the current session, but also in the customer's account itself. This ensures the customer's preferred currency is automatically pre-selected, no matter from where they log in.
Install using colinmollenhour/modman.
Most of my repositories posted here are projects created for customization requests for clients, so they probably aren't very well documented and the code isn't always 100% flexible. If you have a question or are confused about how something is supposed to work, feel free to get in touch and I'll try and help: info@mobweb.ch.