The most popular patronage service for supporting webcomics artists, you probably already know it. → Patreon.
A free/libre alternative to Patreon designed for more privacy and lowest transaction fees. → Liberapay
An alternative to Patreon using euros with an interface translated into French, Germans, Spanish. → Tipeee (in French)
The well known payment system that supports online money transfers with many available currencies. → Donate via Paypal.
Free of charge within Europe and works worldwide:
Address for gifts
Here is an address where I'll receive your boxes and letters:
David REVOY au Cabinet Dentaire
135 Avenue des Mourets
82000 MONTAUBAN - FRANCE