How do I put the equity built up in my primary home to work?

Wife and I own a home that's currently has built up about $600K in equity. This is the only home we own and we expect to live in this house for 2-3 more years before upgrading to a bigger home as our toddlers grow older.

What is the best way to put this equity to work? Should we get a HELOC and then invest that in something else or another rental home?

For background, we have no other debt, have 6 months of savings in cash and we maximize our 401(k)s and post-tax savings every year.