The easiest and fastest way is to back up your guests like hardware servers. You can keep your standard backup procedures in place and thereby continiue your backup business without any change. The drawback is, that you may need backup liceneses for every guest (depending on your software and its license model).
Are you looking at going directly to tape? If you have an intermidiatary backup location, there are 3rd party products like http://www.esxpress.com/ and http://www.vizioncore.com/ that produce backup software that will take a snapshot of the VM and then backup the VM to a network location. There are also some free scripts here - http://www.vmware-land.com/Vmware_Links.html#Backups. esXpress does provide a free version that does full backups.
If you are talking about the guest OS i would suggest using Symantec backup Exex system recovery. You can then easy restore the data to a new VM with VMware convertor (for version 7 you need the latest version of VMware convertor 3.0.2) . You may want to backup SQL/Exchange data using a different method, but to restore the OS this is a good option
You can also copy each VM folder located on the VMFS share. this however would require you to shut down the VM first.
ESXpress is very easy to use, very inexpensive and works great. I use it at several customer sites for backup and DR. Check out http://www.esxpress.com.
