The first alpha release of the upcoming Typo3 4.6 has been made available to the public. Typo3 CMS 4.6 is due to be released in stable around October, 2011 so if you are interested in assisting them with meeting this target, please download and test this alpha and provide your feedback and bug reports.
This alpha release incorporates the following changes from 4.5:
The release plan for 4.6, the schedule and the planned projects are detailed in the project wiki on forge.
More information can be found on their home page: http://news.typo3.org/