Excellent good to hear!
As far as American companies go I don't know much about them, but you want to look for a big company, with a high turnover and a BIG product base for you to sell from.
Look for something that you can talk to a client about and then go away and find something that suits his particular needs rather than just going for a job where you are selling one straight product. The advantages to this are obvious but you will also improve your negotiation skills, deal with people in a high level of business and use your brain to match their needs to something you are selling.
When questioning a company, ask about the directors sales experience and the companies that they have worked for. Ask for references if you feel the need. The chances are that if you find a director that is excellent at sales, they will have a lot of good advice for you.
Also, try to pick a company that is selling something that you believe will actually be of benefit to the client. If you have 100% belief in the product you are selling then the client will be swayed easier because of your enthusiasm.
This sounds like pretty obvious stuff but if you find a company that completes each point and you end up with good training, you will end up being in the top 5% of salespeople.