Are any of you aware of any brokers that provide API's for trading (that I could hook up to my .net application) AS WELL AS provide a mock money account?
I have searched around on sites for this question but surprisingly haven't gotten an answer to the latter part of the question. How can us developers even test our trading apps if well known brokers such as TD Ameritrade, IB don't provide fake money accounts.
In general trading vendors / brokers will never post API to the open world, especially for trading activity. This is usually a violation of some SEC law or some regulatory rulings that keep this this way.
If you really want to build an app on top of those services you would need to enter into a contractual aggreement with them.
Working for a company that trades I would not expose my API's to the general public either.