I will argue that the best time to rebalance during the year is at a market high or a market low. A good time to tax-loss harvest is near the low for the year.
Obviously, the OP is watching the details of their investments (otherwise they wouldn't have started this thread). Many folks get caught up in the euphoria of 52-week highs without thinking about what to do with them. Those dates I gave were market highs and lows so far for 2010.
So if you are watching the details of your portfolio enough to start this thread, what are doing with the information you garner? Small cap value and REITs were up higher YTD back in April than other asset classes. Did you rebalance out? International funds were down lower in May-June than other asset classes. Did you rebalance in?
Furthermore, the OP writes:
All three funds have seen many peaks and valleys this year, providing many opportunities for rebalancing them.
That's why I am asking this.