Download for free Multi-Store Appropriate Store Switcher – an extension for Magento
Use this extension for Magento to automatically detect the location of your customer and suggest the best store to the customer when they first visit your website. In a multi-store environment where customer may land on any of your store, use this extension to notify the customer of your other store that best match their location in terms of their familiar currency, language, themes and other settings that are configurable in Magento admin. The visitor location is detected from IP address, using MaxMind Geo-location framework.
To derive maximum benefits from Magento multisite instance where multiple domains have been assigned to Magento store (configured in admin), customers are notified of their current store. However the customer is presented an alternative Magento website/store (that you pre-configured in admin), which best match their profile, based on their current geographical location.
The complete installation instructions and product documentation is available here: http://www.mageperfect.com/multi-store-option-presenter-for-magento/
See the live demo here: http://siteswitcher.mageperfect.com/