Congratulations, SO!
I have to say that you guys can provide some kind of certificates, merchandise or some kind of trophies to the reputed users as a thank you gift like YouTube sends to its reputed channel owners.
The point is that these kind of goodies helps in keeping alive the spirit of an individual and moreover pushes the new users to work hard and contribute more.
By certificates I mean that online certificates that can be downloaded as a pdf file so that we can take printout of the certificates.