http://www.cbssports.com/mlb/news/the-exposnationals-franchise-now-has-mlbs-longest-pennant-drought/
Here is the year of each team's last pennant:
2016: Cubs and Indians
2015: Royals and Mets
2014: Giants
2013: Red Sox and Cardinals
2012: Tigers
2011: Rangers
2009: Yankees and Phillies
2008: Rays
2007: Rockies
2005: White Sox and Astros
2003: Marlins
2002: Angels
2001: Diamondbacks
1999: Braves
1998: Padres
1993: Blue Jays
1991: Twins
1990: Reds and Athletics
1988: Dodgers
1983: Orioles
1982: Brewers
1979: Pirates
Never: Expos/Nats and Mariners
The Mariners joined the league as an expansion team in 1977, the Expos/Nats in 1969, so the Mariners pennant drought is shorter than the Expos/Nats by default.
Expos got screwed by the strike shortened season.
So over the last 12 seasons, half the MLB teams have made the World Series.
Longest current World Series championship drought
Seasons Team Last won Last appearance
107 Chicago Cubs 1908 2016
67 Cleveland Indians 1948 2016
55 Texas Rangers never (franchise began 1961) 2011
54 Houston Astros never (franchise began 1962) 2005
47 Milwaukee Brewers never (franchise began 1969) 1982
47 San Diego Padres never (franchise began 1969) 1998
47 Washington Nationals never (franchise began 1969) never
39 Seattle Mariners never (franchise began 1977) never
36 Pittsburgh Pirates 1979 1979
32 Baltimore Orioles 1983 1983
31 Detroit Tigers 1984 2012
29 New York Mets 1986 2015
27 Los Angeles Dodgers 1988 1988
26 Oakland Athletics 1989 1990
25 Cincinnati Reds 1990 1990
24 Minnesota Twins 1991 1991
23 Colorado Rockies never (franchise began 1993) 2007
22 Toronto Blue Jays 1993 1993
20 Atlanta Braves 1995 1999
18 Tampa Bay Rays never (franchise began 1998) 2008
14 Arizona Diamondbacks 2001 2001
13 Los Angeles Angels of Anaheim 2002 2002
12 Miami Marlins 2003 2003
10 Chicago White Sox 2005 2005
7 Philadelphia Phillies 2008 2009
6 New York Yankees 2009 2009
4 St. Louis Cardinals 2011 2013
2 Boston Red Sox 2013 2013
1 San Francisco Giants 2014 2014
0 Kansas City Royals 2015 2015