There are lots of folks teaching the various niches of voice over. One of the most qualified is animation voice legend-Pat Fraley. Over the years, he's voiced thousands of cartoons. Years ago, I ordered his cassette course (remember those?) and was beyond impressed. Now, if you have a sincere desire to explore with Pat, you might be thinking, "But I live in Minneapolis and he's in LA!" Good news. He has home study courses as well as remote teaching/coaching over the Internet. Here's a short, cool interview with Pat running through a few of his voices. It runs about 8 minutes.
Go to his website at pat fraley.com to see all that he has to offer, which goes way beyond just animation. He also has regular course offerings on audio book narration which has been a booming segment of voice over for years now. There's a "free stuff" section you might want to check out. And be sure to click on "demos" to hear Pat's amazing animation demo.