I'm thinking about starting to put together Red Sox team sets. Haven't decided which years or brands to focus on yet
Recently I've been compiling a HOF binder, one card for each guy. Not focusing on high end or vintage or RCs for this one--it's more just about learning about the lesser known guys and having something pretty to flip through. So most pre-70s players in this set are just newer cards from the random reprints and tributes from modern sets. Some of the lesser known Negro Leagues players are proving difficult to locate though.
Soccer:
I've got a start on some of the various World Cup sets going back to the 90s. Haven't decided how thorough I plan to get with those though.