DISCLAIMER: I am not a trained money manager or whatever, just suggesting what I think is good. No liability assumed for the use of my advice.
I think that while it may not be risk-free, the stock market could work to your advantage. Don't go all in. Say half of what you have or what you feel comfortable with, and put the other in something more secure. Companies that have been around for a while (a few years minimum I think) that are just in a slump. If you have a few years, you may be able to watch them grow back to what they were with a substantial profit for you. The only problem may be that they go under, so be sure you choose one that has good potential. Don't just go for one, spread the wealth.
I think that investing in a small startup company might be something fun to do, and something that may pay out well.
Other than that, I can't think of anything that'll make you a lot of money investing. No risk is little reward. Risk is big reward, but potential of failure. I hate to say it, but if you want a house... get a trailer! You get a little house, and you get a nice community and no messy investments. Watching too much Trailer Park Boys...