Thanks to SteveGo's recent posting, we have been alerted to Schwab's hidden costs for trading bonds.

My own case is rather complicated. First of all, I don't like to put all my eggs in one basket. Secondly, due to a transition from a work-related 401K setup to the PP, my portfolio is distributed among several mutual funds, brokerage houses, TreasuryDirect and private holdings (i.e., gold coins.) Shifting funds and money between these entities is getting rather complicated, and the fact that some of them involve traditional and Roth IRAs adds to the complexity. I imagine other PPers are in the same boat.
Any suggestions as to the best combination of ETFs, mutual funds, etc., to simplify portfolio rebalancing while keeping costs at a minimum?