Transcribbler is a Mac OS X text editor with extensions for audio/video transcription. It doesn't do voice recognition, it just helps you type as quickly as possible using customizable keyboard controls and word/phrase abbreviations; its main difference from other similar tools is that you can easily switch between multiple abbreviation lists or use several at once, and abbreviations can be extended with commonly used suffixes.
It uses basic Cocoa API components for text editing, and QuickTime for audio and video playback.