How do you know which securities or stocks are marginable?

I'm trying to buy some more stocks, and I have deposited $5k into my etrade account. I have used up most of the initial $5k, but in my balances, it says that I still have about $5.4k in Marginal Securities Purchasing Power and about $2.7k in Non-Marginal Securities Purchasing Power. How do I know which stocks are Marginable? price ranges? Thanks all.