Photo bus cards
Have you seen the "hockey rink" writable CDs?
They fit into a regular 2" x 3.5" North American business card format.
You can put e.g. a small website on them, as well as normal printing on one side.
A bit more expense, and work to create, but can be good attention-getters & info-deliverers.
"hockey rink" cds
|Black on White by RaVN11|
|Hummingbird and Bee by dibilio57|
from A Big Year - birds
|xheneta iseni _for DPReview by Mike Slade|
from - My Fair Lady - (Portraits in Full Colours Only + A Border)