Are there any online brokerages that are known to pay good interest rates on the cash part of a stock account?

I am talking about the money in the account that may be used to buy a stock. Brokerages usually pay you interest in the cash part. Which brokerage tends to offer the best rates for this?

That is something you should always consider depending upon the type of investing or trading you do. Brokers have to make their money somehow, so brokers with lowest trade fees tend to pay less interest on idle cash. But that info is often very hard to find (if even publically available) before you sign up for an account. Or in some cases you have to specifically ask them (unpublished anywhere).

For example Fidelity pays a decent interest rate on core cash in retirement accounts (IRA's, etc.). But in taxable accounts you have a number of choices from unpublished variable (based on balance) by default, to published higher taxable interest, or federal (or in some states, state) tax free at less interest, but federal (and maybe state) tax free. Although, their stock trade fee is kind of high unless you have at least $50,000 in assets in your own accounts and/or a certain number of trades per year.

So if you have an account with a low interest rate on cash, you may need to more proactive stashing your cash in something (money market or dividend paying ETF's) and freeing up some cash in advance of wanting to buy something.

Or you are perfectly free to have 2 accounts at different brokers for different types of investing or trades, with one for longer term investments (that pays more interest on cash), and another with lower trade fees/less interest for learning short term trading techniques. That is what I am doing with my IRA's.

Try Ameritrade (or whatever it is called these days). They have historically paid pretty high APRs on cash balances. I worked for Scottrade (and am still a client), and their APRs are low, but they are a great company to do business with.