Ameritrade has a cash sweep option called the Total Asset Plan (TAP) which offers a significantly higher interest rate on cash than the default Ameritrade cash sweep option. When you first setup an Ameritrade account, you are put into a cash sweep option that pays less than 1% interest. By contrast, as a participant in the TAP, the cash sweep is offered through money market funds at "The Reserve" (website: ther.com). There are a variety of taxable and tax-free money funds available. For example, the taxable Primary Money Market fund pays about 4.4%. Personally, I chose the California Tax-Exempt fund which pays about 2.4%.
But, don't go looking for the Total Asset Plan on the Ameritrade website; it's not there. In order to setup this account, I needed to talk to a customer service representative. In fact, I would not have even known that the TAP option existed without speaking to a real person at Ameritrade. I don't know why they keep the TAP a secret from most investors.
Lastly, having gone through the application process once, I now know where to find the TAP application on the Internet. However, since this is a "hidden" option (that Ameritrade doesn't want the average person to know about), I would suggest calling Ameritrade to inquire about it.