I'd like to nominate @luzcypher. The amount of work that guy has done for the community over the last year is huge & its about more than just entertainment.

The open mic competition here has:
Improved my confidence.
Encouraged me to develop new & existing music skills
Helped me to interact with new people.

If those things can be true for me then I'm sure that many of the ever growing number of participants have felt the positive effects in a similar way.