After announcing vSphere 5.0 in July this year, VMware now has made vSphere 5.0 which consists of ESXi and vCenter Server generally available for download.
When VMware introduced vSphere they also introduced a new licensing model based on the amount of memory allocated for a virtual machine when it is powered on. This caused a lot of discussion dubbed "vTax" after which VMware decided to update its Licensing and Pricing terms, this still is causing a lot of discussion for certain scenario’s though.
vSphere 5 contains about 140 new features, which are mentioned here and comply with the feature list which leaked in April this year.
Some documents to consider reading before updating/installing are: