Jimmy Walker/Jalen Rose: Both strong NBA players. Jalen had a longer career and more seasons with impressive stats, so it seems arguable he was the better NBA player in his time. Mike Bibby, mentioned earlier, was (still is?) a better NBA player than his father, Henry.
Pete Maravich's father, Pete "Press" Maravich, actually played in the NBA's predecessor for a season, so Pete qualifies as well as a vast improvement on his dad as an NBA player. (Had to look this one up). Kiki Vandeweghe's father, Ernie, was a Knick in the early days, making Kiki a qualifier as well.