These 3 ETFs are great low-cost options to hold for the long haul.When the market is on a tear, it's tempting to hold back and wait for a pullback. The problem is that waiting usually works against you.History shows that new highs aren't rare, and many times stocks never revisit those lower levels again. A J.P. Morgan study found that since 1950, the S&P 500 hit a new high on about 7% of trading days, and nearly a third of those times it never traded below that level again. That's why dollar-cost averaging ...