In 2006 Adam Dunn joined an exclusive club when he became only the eighth player since 1960 to hit 40 homeruns without driving in 100 RBI or scoring 100 runs. The list of players to accomplish this feat before The Dunner is exclusive, but as you can see below, Adam Dunn's 2006 season was a unique one.
Unlike Dunn, all of the other players on the list had seasons which ranged from the very good to the elite:
Ken Griffey Jr. and Matt Williams joined the club in 1994, and were on pace to challenge Roger Maris' single season homerun record when the season was abruptly cancelled due to strike after 112 games.
Darrell Evans was an aging veteran in 1985 when he joined the club, accumulating on 505 at-bats but putting together a 1:1 walk to strikeout ratio (85:85) along with an impressive .875 OPS despite his .248 batting average.
Hank Aaron and Davey Johnson were teammates on the 1973 Atlanta Braves, a team which also featured Darrell Evans, oddly enough. That teams featured four players with 80 or more RBI and 80 or more runs. Not only were the runs and RBI spread well enough around to keep Aaron and Johnson from getting 100 of either despite very good seasons, but Aaron only played 120 games at the age of 39 that year, indicating that he would have had well over 100 runs and RBI if he had not missed a quarter of the season.
Petrocelli's 1969 season was an excellent one, and he would have easily garnered 100 RBI if not for missing 8 games and gathering a comparatively low 535 at-bats. Likewise, Harmon Killebrew would have collected four more RBI in 1927 had he not missed 20 games and batted only 515 times.