Many hosts offer block-level backups services, for a price.
But IMO it totally depends upon the services installed on the VPS. If its a database server, generally these already have extensive support for performing automated backups. So all you need do is write some scripts that execute each night etc.
If it's an application server with very little custom configuration, then you probably don't need it backed up at all. If the worst was to happen, just reinstall and spend a few minutes reconfiguring. Done.
If however it's an app server with lots of custom configuration, and there is no obvious way to backup that configuration (like say an XML file or something) then yes a block-level VPS backup is probably what you'll need.
I view block-level VPS backup as the last resort.