If you are looking for a single Vanguard fund, the target retirement income and target allocation income (name?) funds, with 30% and 20% stocks respectively, are pretty stable while producing decent returns. You could argue that they are not tax efficient, but you will still be making more money usually, with little risk of significant loss.
Personally, I plan to save for a house by starting with 100% stocks (VTI, VEA,VWO) and use the value averaging strategy by buying or selling each of these to create a 2% real increase per quarter. The rest of the money I will put in treasury bonds, such that in about 8 years I will have a about 20% stocks and 80% bonds, but the stocks will have been purchased as efficiently as possible.