The best place for long-term storage of seeds is your freezer; but that requires containers that are completely air-tight, otherwise the seed will desiccate (as in be freeze-dried). Baby food jars might work, as would any other jar with a rubber seal. Ball jars are good for this, you can put a lot of envelopes into one.
But I think that the best method for preserving seeds is the heat-sealed foil packs. Several seed companies carry them, including Seed Savers and Southern Exposure. You can also re-use foil-lined chip bags, if they are cleaned out.
Remember that if seed is frozen, it must remain sealed in its container after removal from the freezer, until the seeds (and the container) reach room temperature. Failure to do this can cause condensation on the seeds, which will quickly destroy them.