Alternatives to XML?

I have grown to really dislike XML as a comunicating protocol/data serialiser. It is very verbose and inefficient, especially for mobile use. Its main advantages are: it is ubiquitous, and there are many free tools, parsers, marshallers available for any languages.

Assuming you have control both to the server and client, what would be a good alternative to XML? I thought about Json, but I don't like its syntax. What's your experience with these alternatives?