Do you want to index US stocks, international stocks, or bonds?  Do you want stocks of all sizes?  Do you want bonds of all maturities?  What's your tax situation - are you investing in IRA, non-IRA, or a mixture?  Is your tax rate high enough to look at municipals?  You have to make these choices, because Vanguard index funds are all run according to the same principles, so what matters is your target. 

Once you know what you want to index, you should compare costs for ETF (higher trading costs but lower holding expenses) and mutual funds (lower trading costs but higher holding expenses).  Both are very cheap from Vanguard so you can't really go wrong.  You can index just about anything, included a balanced fund. 

If you want active management, the first place to look is VWELX (more aggressive) and VWINX (more conservative).  Solid long history and low (but higher than index) costs on both.  Likely to outperform other funds with the same amount of risk, may outperform stock/bond index but no guarantee.