Kevin, that is a tough question. I know Inventors that have built a site and sell their product themselves and do very well. If your product is protected by a patent that is one option. If it is in the beginning stages and has no protection you do not want to post it on a website of any kind since you may put it in public display and ruin your chances of getting a patent down the road.
The Inventors that are building a business around their product on the web live or die based on traffic to get sales. Then you have websites that charge you a monthly fee to post your invention along with several hundred other inventions. Those same websites normally offer other services such as building your promo page and doing enhanced photos/drawings of your invention. All for an addtional fee. The problem with these sites is that they don't have the tie-in with companies actively looking for products. So, you are posting your invention on a site the company knows nothing about in the hopes that they will magically find the site and scan through the hundreds of inventions there and find your one particular product. Unless you are actively pitching your product and directing any interested companies to your page on that site I doubt you will see much success. Those sites don't have the direct contact and connections to make it work. They are basically warehousing your invention portfolio for you.
An Inventor I met that used that system, had it posted for two years without any results because he was relying on the company finding him. I took his information sent it around and within 3 months he had a company interested and offering him a licensing deal.
You have to keep in mind that most companies are not going to pay an employee to scour the internet to find them a great idea they can manufacture. Getting your name out there is half the battle for companies to take you seriously. I use my website as a business card when I talk to companies. They can look at my successes while we are on the phone and see that I work in a wide variety of areas. So, even if their industry isn't one I have worked in before they can see that I am versatile and will be more open to giving me a shot.
This industry is more about knocking on doors and doing your homework than anything else.