I am in India and its pretty customary to give speakers tokens or mementos of appreciation especially in cases where he or she has come as a guest speaker (at no fee/charge). The usual plaque or salver is what we often give, which they proudly display on their stands back home or at office.
Off late I have tied up with a not-for-profit organization that is into afforestation and also aide smaller farmers in growing saplings. So what we do is, instead of giving a plaque or anything that in reality is pretty useless in itself we have started issuing ‘Green Certificates’ via this Not for profit org. They charge us per sapling – so if the speaker is a keynote speaker we ask the organization to plant 10 saplings in his name and they in turn provide us with a QR code. We get certificates designed and embed the QR code in it stating that In appreciation of XYZ 10 sapling have been planted in XYZ forest/farm…the QR code actually leads him to a landing page which has the google map coordinates where the plants are and photographs of the actual saplings as well.
People seem pretty kicked about receiving this.