Rydex Funds, RYVNX and RYVYX (Venture 100 and Velocity 100), accounts for twice the action of Nasdaq 100. Venture 100, RYVNX, moves against Nasdaq 100, so you are "shorting". If Nasdaq 100 goes down 1%, the fund will move up 2%. Same applies with Velocity 100 except you are going "long."
They have other funds as well that moves same as Nasdaq 100. You can open account with Rydex Funds and incur no fees (annual fees though? Not sure) but you have to have 25k to open an account. You can trade them through a broker as well but you will pay commissions and might be charged additional fees such as 180 day "short-term redemption fee".
Since I don't like being tied to enter a position at the end of the day, and like the flexibility of Cubes, you can go with full margin and achieve similar results, twice the gain/loss.
Hope this made some sense.