What if you invest in yourself ? Or a business you know ? Bitcoin investments dont really exist because bitcoin is so volatile I guess.
You can count altcoins as investments too. Gambling is much better then HYIP though.
There are gambling sites with investment feature, you can invest as low as 10 mBTC. you won't profit much though if you invest low amount, the bigger amount you invest the bigger profit you'll make.
Instead of playing gambling games in Casino, I suggest to invest in the casino bankroll. There is more chance of winning if your money is in the Casino bank roll than your own bankroll and use them to bet against the house. We have seen several gambling casino that gave a positive profit to their bankroll investors.