Since the vCenter Client no longer is bundled with an ESXi host installation, I´ve compiled a quick list of direct download URLs for the most recent clients.
Update 17th September 2014:
VMware has published the official list inknowledge base article KB2089791, use that as the official list going forward.
Remember, the client download URL is still available from the vCenter server, if you point your browser to it.
Another way of getting hold of the client is from the vCenter ISO file downloadable from vmware.com.
10. September 2014: Table updated to include new version for 5.5 update 2