My original thoughts were to dump a bunch of money into Vanguard Index Fund. Low fees, match the S&P and be done with it.
This is a good idea if you have a 15+ year time horizon. Especially if you're contributing to it on an ongoing basis.
Now of course we have the second greatest run in the last 10 years to make up for it, but what happens if you're closer to retirement when a 2008 hits?
You should not be fully invested in equities if you're closer to retirement. Most people will gradually shift assets from aggressive to conservative as they age.
If you have 1 Million in the market and start taking distributions at 65, eventually your account value will decrease to $0. Year 1 if you take out $100k, you're down to $900k + whatever interest you've gained, Year 2 $800k and so on until you get to $0.
If you're allocated properly and manage your distributions accordingly, there is no reason for your account to go to zero.