I appreciate the thoughts. I wouldn't say exactly that I have a "known liability in a known window of time", as five o'clock shadow put it, because purchasing a house will be entirely our decision, and one that we can make when we feel the time is right. We can also control the amount of money that will be needed, by choosing to purchase a more or less expensive house, or choosing to put more or less money down (we will be shooting for more than 20%).
So I'm not completely risk-averse, and The Lending Club and junk bond funds are two options that I was considering, but I've been hearing so many complaints about the Lending Club lately, I'm starting to shy away from it. On the other hand, SJNK seems like a reasonable choice for at least a portion of my money. Current yield is 6.42%, which is 36.5% compounded over 5 years. The ETF currently trades at $40, and the lowest it has ever been is $27 at the market's nadir in 2008, or 32.5% below today's price. Anything can happen, but I would be comfortable assuming the risks with at least a portion of our money.
I have about $10,000 I can invest right now, and the remaining money will be saved over the coming years. I may start with a lump sum invested in a riskier, but hopefully more profitable, junk bond fund, while putting future savings into safer bets, like Treasuries.