I'm writing this as the Arizona-Milwaukee game is still going on, so we know the ALCS teams but not the NLCS teams.
Through 2010, six different AL teams won the last 6 pennants. There were 8 different winners in 1981 through 1988. That's going down after this year. If the Rangers win, they'll be the first AL repeaters since the Yankees in 1998-2001. If it's the Tigers, we'll have had five years with 5 different pennant-winners.
In the National League, if the Phillies don't make it we'll be up to three different pennant winners in three years, so not much going on there.
We're also on a string of six different World Series Champs in six years. One live team will threaten that by the end of the day, either the Cardinals or the Phillies. The longest consecutive string of different WS winners is nine, also in the 1980s (1982 through 1990). So if it's either AL team or the winner of the D'Backs/Brewers game, we'll be up to an impressive seven years; the Phillies gets it down to three, while the Cardinals would make it five.
For what it's worth, the Super Bowl record is, if I'm counting correctly, six different champs in six years, while in the NBA they've made it up to five.