iOS (jailbroken): Google recently updated its Search app on iOS to include Siri-like voice searches. If you like Google's offering better (or can't get Siri on your older device), free tweak NowNow lets you launch Google's voice search with a home button shortcut, Siri-style.
After installing NowNow, head to your Settings, scroll down to NowNow, and choose the shortcut you want for Google's voice search (I used a triple-tap on the home button). Using the shortcut will give you quicker access to the Google app than you can get from the home screen. Check out the video above from AppAdvice to see it in action.
NowNow is a free download for jailbroken iPhones, available in the BigBoss repository.