I would not expect a gift.

The only thing I would want is a sincere 'thank you', or maybe a cheque/check for $1,000,000 :)

I would love to receive a beautiful letter.

Well, in general I like gifts to show that you have thought about what you should buy, so rather something small and relevant and personal, than something expensive. My father always used to give me money for my birthday and say I should buy something myself. That is perhaps not totally relevant here, but I hated that. So my advice is to try to find out what the person likes and then make something out of that.

I think the best presents are the ones that mean something. It doesn't have to be very expensive, but have a special meaning. That's the kind of present that I would like to receive.

In my case, if I would have to send a gift to a language partner I'd pick something from my own culture. A set to drink "mate" seems to be a good option to pick as a gift from Argentina :p

@Sandy liu @seven Book is something I always choose as a gift for my friends…. But of course in my native language
@ Giovanni ummm I’d never thought about that….but there must be something like that.
@Marc Exactly that’s the thing I always concern about….Thanks for sharing that 
@Bertram So nice…I really like that, letter shows feeling in best way.
@ Ahmed not physical presents are much easier.
@ Richard How satisfied you are )))….. 1,000,000 is not that much, the friendship worth more ….haha