Try Audcity . http://www.sonicdownloads.net/download/Audio/Audacity/?f=inCAk0Xte&a=7378&adid=742700073

its free, it has a voice pitch changer and other effectd you can do with voices and sound. like echo and  bass. so you can use your own voice in videos and manipulate the the pitch. Thats what I use instead of  robot voice or electronic.sounds  to me it sounds much better, those electronic voices sound so phoney..

when I can and  i get a chance i try to use Kids to do the voices overs .. for some reason kids voices always sound better for characters. so when i need kids i call my teacher friend at the high school and she'll ask the kids for me in her class if anyone wants to do characters voices .. never a shortage of kids wanting to do cartooon voices. and now thats I have used kids from the high school  a few times  I also don't have a shortage of volenteers anymore when i need characters voices. :)