I never collected any cards past 1965, the year I quit collecting as a kid. My primary interests are in 1930's sets but I have completed 1950's Red Man and Red Heart sets.
About 8 years ago, I started collecting George Brett cards whose career covered 1975-1994. These are years that I had never followed or had any interest in collecting. I buy these cards usually when I get bored or there is a lull in my main collecting activities.
I thought it would be a nice goal to find 100 different George Brett cards, breezed right through that number, and now am up to 230. There are probably a few thousand, but I do not even keep a want list because this is one collection I have been succcessful in keeping myself from obsessing about getting every card. I have found this to be a fun way to learn a little about modern cards.
Most of the cards, even in gem mint, are affordable. I have been able to resist spending $5,000 for the rookie card.
http://imageevent.com/rgold/rgoldscollectiongeorgebrett