The S&P 500 is still a smart all-around option, but there's good reason to start thinking about other index funds.

There's never really a bad time to buy the Vanguard S&P 500 ETF ( VOO 0.59% ) . But there are better times than others: It's better to buy on a dip than at a peak, for instance. If your goal is to simply plug into the broad market's long-term performance, though, your best bet is just stepping in whenever you have some otherwise idle cash you're looking to put to work.

Every now and then, though, it makes sense to look beyond the most obvious of ETF picks and act strategically, even if you want to (wisely) remain passive; a different index fund could bolster your long-term performance.

With that in mind, rather than committing any more money to the Vanguard S&P 50

See Full Page