11. A speech recognition system comprising: at least one processor; an analog-to-digital converter configured to convert an analog signal corresponding to speech input received at a microphone into a digital signal corresponding to the received speech input; and memory storing program code that, when executed by the at least one processor, causes the system to perform, using an initial recognizer, an initial speech recognition pass on a portion of the digital signal corresponding to an input speech utterance of the speech input to determine i) an initial recognition result corresponding to the input speech utterance, and ii) a reliability measure reflecting a per word reliability of the initial recognition result, perform, using a re-evaluation recognizer subsequent to completion of the initial speech recognition pass, a re-evaluation recognition pass on portions of the initial recognition result where the reliability measure is low to determine a re-evaluation recognition result corresponding to the re-evaluated portions of the input speech utterance, and determine a final recognition result based on the re-evaluation recognition result if any, and otherwise based on the initial recognition result; wherein the initial recognizer and the re-evaluation recognizer are complementary so as to make different recognition errors.
11. A speech recognition system comprising: at least one processor; an analog-to-digital converter configured to convert an analog signal corresponding to speech input received at a microphone into a digital signal corresponding to the received speech input; and memory storing program code that, when executed by the at least one processor, causes the system to perform, using an initial recognizer, an initial speech recognition pass on a portion of the digital signal corresponding to an input speech utterance of the speech input to determine i) an initial recognition result corresponding to the input speech utterance, and ii) a reliability measure reflecting a per word reliability of the initial recognition result, perform, using a re-evaluation recognizer subsequent to completion of the initial speech recognition pass, a re-evaluation recognition pass on portions of the initial recognition result where the reliability measure is low to determine a re-evaluation recognition result corresponding to the re-evaluated portions of the input speech utterance, and determine a final recognition result based on the re-evaluation recognition result if any, and otherwise based on the initial recognition result; wherein the initial recognizer and the re-evaluation recognizer are complementary so as to make different recognition errors. 15. The speech recognition system of claim 11 , wherein the initial recognizer and the re-evaluation recognizer use one of different complementary acoustic models or different complementary language models.