You're possibly not aware of the technical terms? You didn't ask for specific substances, but i think the Nist webbook has it for most components in the tab Gas phase ion energetics data. Apart from the problem of finding the data, what do you expect from it? As far as I understood are you trying to implement ionization by an electrical field. I don't think, that the ionization potential directly shows in this situation. It applies to phenomena with direct energy transfer to the molecule, e.g. electron impact or photon absorption.
As a brief comment, the periodic table of elements listing is meaningsless for the said problem except for helium. Atmospheric gases are molecules and have quite different ionization potentials, e.g. N2 15.6 eV. That's why a photoionization detector is able to detect organic compounds.
The two first links are nice compilations (save you from picking the info at NIST webbook). I would prefer to hear what the original poster is exactly looking for.
Non toxic gases - Maybe nitrogen as we are used with air, but too much is not healthy either.
Non toxic gases + ionization - Sounds unhealthy for any gas.