I hate to leave my sync on and really only want it on when I send a email. Unfortunately, the emails using gmail will not be sent unless you go into settings and make a sync. Does anyone know an app that will automatically sync your gmail when you send a email?
While not exactly what you're asking for, you can use WiSync and/or WiSync+Locale to control your phone's auto-synchronization behavior. WiSync is free and available from both the Android Market and SlideMe.
If you want an application which readily allows full control over synchronization with a multitude of triggers, even via a scheduler, consider WiSyncPlus. There isn't another application which can save as much power and has as many synchronization centric features as WiSyncPlus. Its extremely configurable, as you can see from its FAQ. And if you need graphical representation of power savings potential, check out this page.