If you are looking for an invention investor there are three forms of funding you need to consider.
The first form of funding is what I call shoe string investment. Shoe string investment is carefully spending the least amount of money possible to prove the legitimacy of your idea and to get it protected. By definition money is scarce in this scenario. In this case you must follow a proven process to preserve your precious capital. Shoe string funding is best done by the inventor themselves. Not many people will invest in a napkin sketch or just an idea.
There are many ways to get this money but the most common venture capitalists for this type of funding are Master Card and Visa. It is your idea so you must prove it is a good one.
The second form of invention investor funding is the Angel investor. Angel investors are typically average people that have money to invest and usually have some expertise to share. Experienced angels are the best form of investors. These people could be your rich uncle or a local businessman looking for a product to invest in. In my experience angel investors are successful business people that want to be involved in the thrill and reward of a start up business.
Since angel investors typically have had some success in the business world they are going to want a reason to believe that your invention will be a success and make them money. If you pursue angel money always write a business plan first and enter into a contract with that person. A written contract will help to spell out what happens if something goes wrong (it always does) and help to prevent misunderstandings (there always are).
The last form of invention investor funding you can choose to pursue is venture capital. Venture Capital or VC funding is typically the hardest money to get and many times the most expensive in terms of what you will have to give up to get it. VC's always want a well thought out business plan with an exit strategy. An exit strategy lets them know how they will eventually get paid.
For a venture capitalist to be interested in your invention it must be a really big idea. Usually 50 to 100 million dollars in sales as a starting point. An idea this size does not come along everyday and a lot can go wrong going from no sales to 50 million in sales. Since that is the case VC's will want to control over how the business is run and a say in the big decisions.
In the end it is up to you to make sure that any investment dollars are going towards a worthy invention. It is all too common to see inventors spending lots of money on an idea that should have been abandoned long ago. Don't let this happen to you.