Marty Gelinas has scored 3 game 7 ot goals if I'm not mistaken.
Gelinas has three series-ending OT goals, but only one was in a Game 7. The other two (Detroit/Calgary and Carolina/Toronto) were in Game 6.
Since 1940, here is the list of "going beyond the distance" overtimes.
2012-13 - first round - Boston 4, Toronto 3 - Patrice Bergeron
2011-12 - first round - Washington 4, Boston 3 - Joel Ward
2010-11 - first round - Boston 4, Montreal 3 - Nathan Horton
2008-09 - second round - Carolina 4, Boston 3 - Scott Walker
2007-08 - first round - Philadelphia 4, Washington 3 - Joffrey Lupul
2003-04 - first round - Calgary 4, Vancouver 3 - Martin Gelinas
2002-03 - first round - Minnesota 4, Colorado 3 - Andrew Brunette
2000-01 - second round - Pittsburgh 4, Buffalo 3 - Darius Kasparaitis (D)
1998-99 - first round - St. Louis 4, Phoenix 3 - Pierre Turgeon
1996-97 - first round - Edmonton 4, Dallas 3 - Todd Marchant
1996-97 - first round - Buffalo 4, Ottawa 3 - Derek Plante
1995-96 - second round - Detroit 4, St. Louis 3 - Steve Yzerman
1994-95 - first round - San Jose 4, Calgary 3 - Ray Whitney
1993-94 - first round - Vancouver 4, Calgary 3 - Pavel Bure
1993-94 - third round - NY Rangers 4, New Jersey 3 - Stephane Matteau
1992-93 - first round - Toronto 4, Detroit 3 - Nikolai Borschevsky
1992-93 - second round - NY Islanders 4, Pittsburgh 3 - David Volek
1991-92 - first round - Montreal 4, Hartford 3 - Russ Courtnall (2OT)
1990-91 - first round - Edmonton 4, Calgary 3 - Esa Tikkanen
1988-89 - first round - Calgary 4, Vancouver 3 - Joel Otto
1987-88 - first round - Washington 4, Philadelphia 3 - Dale Hunter
1986-87 - first round - NY Islanders 4, Washington 3 - Pat Lafontaine (4OT)
1985-86 - second round - Montreal 4, Hartford 3 - Claude Lemieux
1984-85 - second round - Quebec 4, Montreal 3 - Peter Stastny
1983-84 - second round - Minnesota 4, St. Louis 3 - Steve Payne
1984-84 - first round - NY Islanders 3, NY Rangers 2 - Ken Morrow (D)
1982-83 - second round - Boston 4, Buffalo 3 - Brad Park (D)
1981-82 - first round - NY Islanders 3, Pittsburgh 2 - John Tonelli
1981-82 - first round - Quebec 3, Montreal 2 - Dale Hunter
1980-81 - first round - St. Louis 3, Pittsburgh 2 - Mike Crombeen (2OT)
1978-79 - third round - Montreal 4, Boston 3 - Yvon Lambert
1978-79 - prelim round - Pittsburgh 2, Buffalo 1 - George Ferguson
1977-78 - second round - Toronto 4, NY Islanders 3 - Lanny McDonald
1975-76 - prelim round - Buffalo 2, St. Louis 1 - Don Luce
1974-75 - prelim round - NY Islanders 2, NY Rangers 1 - J.P. Parise
1971-72 - quarterfinals - St. Louis 4, Minnesota 3 - Kevin O'Shea
1967-68 - semifinals - St. Louis 4, Minnesota 3 - Gerry Melnyk (2OT)
1953-54 - Cup Final - Detroit 4, Montreal 3 - Tony Leswick
1949-50 - Cup Final - Detroit 4, NY Rangers 3 - Pete Babando (2OT)
1949-50 - semifinals - Detroit 4, Toronto 3 - Leo Reise
I didn't go before 1940 because the playoff system was too...weird.