I did my own analysis of past results, historical polling, etc. to estimate how much of a "spoiler" effect 3rd party and independent candidates might have had. Here are my conclusions.
2000 Official Results
Bush R 271Gore D 2672000 Results without Nader
Gore D 296Bush R 242_________________________________________________________________________
1996 Actual
Clinton D 379Dole R 1591996 without Perot
Clinton D 367Dole R 171_____________________________________________
1992 Actual
Clinton D 370Bush R 1681992 without Perot
Clinton D 338Bush R 200_____________________________________________________________
1980 Actual
Reagan R 489Carter D 491980 without Anderson
Reagan R 465Carter D 73________________________________________________________________________
1976 Actual
Carter D 297Ford R 2411976 without McCarthy
Carter D 303Ford R 235(Oregon flips to Carter)
________________________________________________________________________
1968 Actual
Nixon R 302Humphrey D 191G Wallace AIP 45
1968 without G Wallace
Nixon R 372Humphrey D 166_______________________________________________________________________
1948 Actual
Truman D 304Dewey R 189Thurmond SRD 38
1948 without Thurmond and H Wallace
Truman D 389Dewey R 142________________________________________________________________
Have also been thinking about 1912, but that's another post.