Mike Aldrete (#158) didn't play for the Giants in 1989. He was traded to the Montreal Expos before the season for Tracy Jones.
Kevin Mitchell (#189) was the NL MVP in 1989. He played left field and batted .291 with 47 HR and 125 RBI.
Brett Butler (#241) batted .283, scored 100 runs, and stole 31 bases for the Giants in 1989.
Joel Youngblood (#304) didn't play for the Giants in 1989. He became a free agent after the 1988 season and signed with the Cincinnati Reds to finish his career.
Donell Nixon (#447) batted .265 in 166 at bats as a backup outfielder in 1989.
Candy Maldonado (#495) played right field for the Giants and batted .217 with 9 HR and 41 RBI in 129 games.
Others who played in the outfield but who didn't get 1989 Topps Giants cards:
Pat Sheridan batted .205 in 161 at bats.
Tracy Jones batted .186 in 97 at bats.
Jim Weaver batted .200 in 20 at bats.