My primary form of rebalancing is through changing where I contribute. Right now I'm low on bonds and a bit high on everything else, so I just changed all of my contributions to bonds. This will continue until I'm back where I want to be.
I also will occasionally sell something and buy something else to rebalance, but not often. Also, this is done inside tax advantaged accounts, so as long as there are all index funds, there shouldn't be any added fees or taxes for doing this. If I had any taxable investments, I would try to structure things so that all of my rebalancing happened within my tax advantaged accounts.