As far as I know, stamps.com is the only one., It's the only one listed on
the MS Office website. Sine I don't have a copy it's difficult to help, but
I had the impression from their web pages that you would have a bit more
control over how their software behaves. For example, when it produces an
"envelope" does it start from a template that you could modify in some
useful way - for example, is there an obvious place where stamps.com is
going to put an address - if so, can you remove it, or set the font colour
to white, etc.? Or might it be possible to print some other kind of item
such as a single stamp, but with envelope stationery loaded instead?

Peter Jamieson

To print Internet Postage only, you need to print the stamp on their
preprinted "NetStamp Labels." You can print one stamp at a time, or an entire
page of stamps to use as you need them. You can specify the amount(s) of
postage, as well. Another option is to print Internet Postage and where it
says "print on" select Label - NCR 903123 - (3-Part). This prints 3 separate
labels: 1. return address 2. addressee 3. postage properties.  Then you could
discard all but the postage label.

Hope this helps!