I've created a Google Sheet to track everything. I don't reinvest dividends (since I want to direct where they go) so once in awhile I update the amount of cash sitting around, or what I purchased. ETF and mutual fund prices are updated automatically.
For me re-balancing is more interesting than performance. Sure, if U.S. stocks are suddenly a larger percentage of my portfolio I know they performed well. But I don't like to get caught up in the performance numbers, so using a spreadsheet I can avoid showing performance numbers if I don't want to see them.