Jeremy Nygaard does a good job keeping track of it; check out the "roster & payroll" link on the top of the page, and keep an eye on the minor league forums. Outside of TD, you can check each leagues' (International,Eastern,etc) website and look up all league transactions - that's sometimes a couple days behind but does get most of the transactions. Also, Baseball America's website has a list of minor league transactions once a week, although it's usually about a week behind the times. Sometimes you get info from twitter feeds for the farm clubs. Bottom line - you just have to dig for it. And even then, Seth will probably get it first.