Magento Community Edition version 1.8.1.0 was released on 11 December 2013.

Magento CE v1.8.1.0 Changes/Fixes.
– Tax Calculation Improvements
– Functional Improvements
– Security Enhancements
– Bug Fixes

Complete list of changes and after upgrade issues can be found here…

Magento CE Download: Magento CE v1.8.1.0