Depends on your income, but if you have the ability to contribute to Roth IRA's, you could do $5500 a year each for the house fund, and withdraw penalty-free when the time comes. That would be 33k in contributions, plus whatever the investment makes. If you're not making use of the Roth IRA's today, that would be a good way to use it. Then save another 9k in taxable accounts and you're there.
In terms of the investments to use, the problem with stocks is that they can be volatile, so the market could be down when you want to pull the dollars out. Bonds less so, but they can still be subject to some volatility. If that happened, would you be wiling to wait a year or two before buying a house for the investment to recover? Most folks would say no. If not, invest in less volatile investments like TIPS or CD's, with lower returns (much lower, given our current interest rates). Saving for a down payment is something you'd like to be predictable over a short run of 2-3 years, which is really tough for market investments.