Talon actually uses Mac's built in STT if you don't have Dragon.
James from http://handsfreecoding.org/ was working on a fork of Dragonfly[0] to add support for Google's speech recognition, but I'm not sure if he still is. There are several barriers to that working well though: additional latency really hurts, API usage costs and (as far as I know) an inability to specify a command grammar (Dragonfly/Vocola/Talon all let you use EBNF-like notation to define commands, which are preferentially recognized over free-form dictation).