I'm working on updating my exhaust on my bike and I'm going to have to build from scratch. While I was tooling around on the internet I came across Engineering Toolbox and they had a link to Google Sketchup.
It's a 3d modeling program that's a hell of a lot easier than any others I've ever used. It's simple, so don't expect it to do extreme stuff unless you go to the pro version. Cool news: it's from Google so there's a free version! I downloaded it and just started dicking around. It's easy to use for basic shapes. I'll have to see if I can do complex modeling on it (and I'm out of practice as it is) but it's fun and integrates with Google Earth. Be interesting to see how well it works and what others are doing with it.