I like to think that I can speak well most of the time. I have a good vocabulary and a voice that carries well. Sometimes I feel it's a bit more nasal than I'd like, but that's not horrible. (You ever notice that your voice sounds far “cooler” in your head than when you listen to a recording of it? In my head, I'm Dennis Haysbert, but everywhere else I'm Gilbert Gottfried. Not really, but you get the idea.)
What I really have trouble with is thinking and talking simultaneously. If I already know what I'm talking about, the words come out pretty easily, but if I'm thinking about it as I go, I tend to stumble and say “um” a lot. It really bothers me, particularly when I'm talking about something technical at work in front of several other co-workers. How do you avoid using filler words when you talk?