I've got 8,056 Cubs cards from 42 different brands listed on a spreadsheet. A random number generator picked five cards, one each from the past several decades.
1950s / 1960s: Topps 1968 #50 Ken Holtzman It was going to be hard for Ken Holtzman to top his 1967 performance in 1968. In part-time duty with the Cubs due to Army commitments (he pitched on weekends when he could get a pass), Holtzman was a perfect 9-0. He was back with the Cubs full-time in '68, but wasn't nearly as good. His record was 11-14 and his ERA rose nearly a run.
1970s: Topps 1975 #352 Darold Knowles This card has an ugly air-brushed picture of Knowles because he came to the Cubs after the 1974 season in a trade with the A's. I had a hard time liking him because the player the Cubs sent to Oakland was my all-time favorite, Billy Williams. His 1975 performance didn't help him gain any popularity either. Though he saved 15 games, he was 6-9 with a 5.81 ERA.
1980s: Topps 1984 #176 Lee Smith This card gives a good look at the imposing Lee Arthur Smith. After an All Star season in 1983, Lee was establishing himself as a premier closer in the National League. He was an important piece of the Cubs division winning team in 1984, saving 33 games.
1990s: Leaf 1995 #341 Jim Bullinger This card shows the one thing I remember most about Jim Bullinger: the funky was he wore his stirrups. He wore them really low, with lots of blue and very little of the stirrup stripe showing. I don't recall any other player wearing them like that.
2000s: Topps Team Sets 2006 #CHC14 Juan Pierre This card is from Topps' first year of the 14 card factory team sets. The picture of Pierre is different that the card in the base set. The factory set was released before his base set card (which was in series 2), so I'm assuming that this one is a photoshop job, since he was picked up from the Marlins in an off-season trade. He played in all 162 of the Cubs games and hit .292. He led the league in at bats and hits, but also led in caught stealing. He became a free agent after the season and the Cubs didn't pursue resigning him.