Also: http://www.speechforsuccess.com/index.html

No personal experience but FWIW: http://www.voicetrainer.com/about-us

I knew someone who took voice lesson to try to get rid of an accent. He said that you need to continue with the lessons otherwise it doesn't really work/stick. Maybe you could also think about taking drama classes to help with presence.

I am a non-native English speaker and speak it with an accent.I am female and combined with my high-pitched voice and natural reticence, I feel I don't sound authoritative. Are there voice lessons geared towards someone like me. Any recommendations?