The next time any of the planets will align with each other is predicted to be in October 2015. The last time at least three planets aligned was in 2011.
There will never be what is called an "exact" planetary alignment because of the different orbits of the planets. It is estimated that there will be another close alignment, meaning about 30 degrees within each other, of all eight planets in 2438, similar to the one that occurred in 1962. Beyond that, it could take millions of years before all eight of the planets ever align in perfect harmony again.