The command list and some extra info.

Download the lates zip file from vmware.com to update 3.0.x to 3.5 (VMware-esx-upgrade-from-esx3-3.5.0-64607a.zip).

Unpack it and place the files on a webserver.

Bring your ESX host to maintenance mode, then log in as root.

Open the firewall to be be able to access your webserver:
[root@esx01 /]# esxcfg-firewall -o 80,tcp,out,http

Check if you got the right files
[root@esx01 /]# esxupdate -n -r http://servername/update info
Product : VMware ESX Server
Vendor : VMware, Inc. ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it )
Release: : 3.5.0-64607
Release Date : 2008-02-16T03:09:39-08:00
Summary : ESX 3.0.x to 3.5.0-77267 upgrade
Description :
This is a bundle for upgrading VMware ESX Server from
version 3.0.x to 3.5.0.
It updates all the RPMs on the system and rolls up all previous patches.
Drivers from ESX 3.0.x that have been superseded by newer drivers will be
removed from the system.
Upgrade paths : 3.0.0, 3.0.1, 3.0.2
Repository URL: http://servername/update

For a detailed list of rpms, use the -l/--listrpms option.

Do the update:
[root@esx01 /]# esxupdate -n -r http://servername/update update
INFO: Configuring...
...

INFO: Installed VMware-esx-vmkernel-3.5.0-64607
INFO: Shutting down hostd...
INFO: Running esxcfg-pciid to update the PCI ID tables...
INFO: Running esxcfg-boot to regenerate initrds...
INFO: Restarting hostd...
INFO: --- TOTALS: 233 packages installed, 0 pending or failed, 5 removed, 0 excluded ---
INFO: Install of ['3.5.0-64607'] is almost done.
INFO: Please reboot the ESX Server by typing 'reboot' to complete the update.

Close the firewall:
[root@esx01 /]# esxcfg-firewall -c 80,tcp,out,http