While this is more expensive than buying "regular" face value stamps, Australia Post's "MyStamps" are a great way to inexpensively brand your business for any letters or parcels you might send, for only 10% more than plain normal stamps.
I've had an amazing result from my customers
You can use any logo or photo or design that you want. I use my business logo.
Didn't even know this existed. Pretty cool, will order some.