VMware released 6 patches for ESX 3.5 including:

VMware ESX 3.5, Patch ESX350-200905401-BG: Updates vmkernel and hostd RPMs Critical updates related to HA failover of VM’s on NFS datastores and invalid license issues. Host reboot required.
VMware ESX 3.5, Patch ESX350-200905402-BG: Updates VMX RPM General update to address a robustness issue with VMX. No Host reboot required.
VMware ESX 3.5, Patch ESX350-200905403-BG: Updates aacraid driver for Adaptec Replaces the Adpatec aacraid_esx30 driver to mitigate potential failure under heavy load on some IBM, SUN or Fujitsu hosts. Host reboot required.
VMware ESX 3.5, Patch ESX350-200905404-BG: Update to tzdata package Updates time zone information for changes in Brazil and Argentina. No host reboot required.
VMware ESX 3.5, Patch ESX350-200905405-BG: Updates Kernel Source and VMNIX This patch updates kernel-source and kernel-vmnix to support the aacraid software driver update. Host Reboot is required.

One of the locations that VMware lists updates is on the VMware Knowledge Base Blog.