With that short of a time horizon, there's not all that much to be gained by having it invested in something with a lot of volatility. I think you'd be justified with having it in something as boring as a savings account.
I accumulated my own house down payment over the course of about three years, and had it stashed in the Vanguard Short Term Investment Grade bond fund (VFSTX). So it earned more than if it was in a bank account, but nothing exciting.