Does anyone know the best route to getting some prototypes of a relatively simple mechanical device manufactured?

I could have sworn I saw a place recently that lets you design things online and then submit them for fabrication. That would be perfect for me, but I can't find it anymore.

Preferably, a domestic company.

metal, plastic, or what??? Complex or simple construction?

First, don't even consider doing anything until you patent it. Whatever company you send it to could patent it and then take your idea after charging you to make a prototype. Get a patent lawyer, and a good one will be able to tell you who to go to in order to get a prototype made for sales.

Mostly plastic.

Circuit Cellar (http://www.circuitcellar.com/) is aimed mostly at small electronics (and used to be the Circuit Cellar Ink column in Byte magazines - if your memory goes back that far), but they have some hardware articles. If you have a decent bookstore nearby, see if they have a couple copies of the magazine. Read the ads all over the magazine! Not every ad runs every month. Also, grab a few copies of Make (http://www.makezine.com/) if they have one.

My first thought echoes Kelraz'; be sure to have your ducks aligned for ownership.

Other than that, hard to say without knowing the complete details whether injection molding or another process would be most useful for your purpose. And all can get spendy, as molds need to be designed, etc. Good luck with it though.

Is RepRap (http://reprap.org) an option?

This is pretty neat, but not quite what I remember seeing: http://www.emachineshop.com/

I would find a local machine shop or if its not to complicated of a thing you can probably build a prototype by yourself or with some friends who are motorheads.

I don't think a machine shop can do it. I'm going to need nylon cord, plastic body, coil spring, etc. worked into it. And, I'm definitely not looking to have to assemble them myself.

I do hope I can find a domestic (or even local) place to do it though.

Is there a reason you aren't patenting it first? Your lawyer will help you find a place to get a prototype made and you won't be super vague with them like you have to be now. Girl I am friendly with from college has been dating a patent examiner for the past few years. He'll tell you all sorts of horror stories of people getting their ideas stolen and not finding out about it until they go to get the patent. It really should be the very first step.

I've been getting the patent in the works too. Trying to get things lined up so that I can move more quickly when it's time.

Glad to hear you have the patent in the works. Nylon cord, coil spring, and a plastic body ... sounds like a fancy new penis pump, and I look forward to being one of your first customers.

Sanchek, if you have the designs in Solidworks or some kind of computer-aided design software, I know a supplier able to do what you need. I'll check our supplier list when I return to work Monday.

Mail everything you have to yourself document wise via certified/registered mail and never open it. not fool proof by any means but it provides you with a time stamped backup for court that adds evidence of idea.

That and Bylimet needs the work.