Below's a list of the 16 unassisted triple plays in major league history (with "player" being the fielder who turned the play, NOT the batter who hit into it):

PlayerPositionTeamDate
Paul HinesCFProvidence GraysMay 8, 1878
Neal BallSSCleveland NapsJuly 19, 1909
Bill Wambsganss2BCleveland IndiansOctober 10, 1920
George Burns1BBoston Red SoxSeptember 14, 1923
Ernie PadgettSSBoston BravesOctober 6, 1923
Glenn WrightSSPittsburgh PiratesMay 7, 1925
Jimmy CooneySSChicago CubsMay 30, 1927
Johnny Neun1BDetroit TigersMay 31, 1927
Ron HansenSSWashington SenatorsJuly 29, 1968
Mickey Morandini2BPhiladelphia PhilliesSeptember 20, 1992
John ValentinSSBoston Red SoxJuly 8, 1994
Randy Valarde2BOakland AthleticsMay 29, 2000
Rafael FurcalSSAtlanta BravesAugust 10, 2003
Troy TulowitzkiSSColorado RockiesApril 29, 2007
Asdrubal CabreraSSCleveland IndiansMay 12, 2008
Eric Bruntlett2BPhiladelphia PhilliesAugust 23, 2009

A few notes:

Hines' triple play is disputed. According to information found on cbs.sportsline.com, runners were on 2nd and 3rd when Hines made a running catch and touched third base for the second out, before throwing the ball to second base for the third out (for what might be a triple play, but NOT an unassisted one). However, many claimed that both runners were past third base when Hines touched it, which would have given him an unassisted triple play, according to the rules of the day.

Due to this uncertainly, Hines is sometimes excluded from lists and counts (leading some sources to say there have been 15 unassisted triple plays in history, instead of 16; I have emailed the Research staff at the Major League Baseball Hall of Fame for clarification).

Wambsganss's triple play was in the World Series. Velarde also turned a triple play during spring training (which, being in an exhibition game, doesn't count as an official record) the same year as his regular season play.

Almost all unassisted triple plays come on a hit-and-run play with runners on first and second (Hines' being one of the notable exceptions). All but three of the them were made by second basemen and shortstops (Hines was a centerfielder, Neun and Burns were first basemen).

Burns, Valentin and Tulowitzki are the only players in Major League Baseball history to have both turned an unassisted triple play and hit for the cycle in their careers.

Note that Cooney and Neun accomplished the feat on consecutive days. Neun had read about Cooney's UTP and joked to teammates that he was going to do something similar during the next game. As luck would have it, he did! And more than 40 years passed before the next unassisted triple play!