I maintain the following bot:

User:SpaceFactsBot
BRFA (Bots: Request for approval)

A sandbox I have been using to develop things (including stuff related to the above bot)

User:Andrewpullin/sandbox

Some useful MediaWiki API sites:

http://ww.mediawiki.org/wiki/API - Mediawiki API docs
http://www.mediawiki.org/wiki/API:Query - Query information
http://en.wikipedia.org/w/api.php - Full API document
http://search.cpan.org/dist/MediaWiki-API/lib/MediaWiki/API.pm - Perl MediaWiki:API documents