I think a good place to look through is the league leaders section. With OOTP5 you can quickly pull up a player card, so it makes it easy to study the players that catch your eye. I usually look at the leaders in all the big categories, and then pull up the player's statistical history and see how they've fared in the past. I mean, if you wanna familiarize yourself with the league, you gotta start with the good players, no?
Another thing I do is, I always go through the news events and pull up the players involved...ie. players of the week/month, guys who just had a great game, or guys who've been injured.
Sometimes, when the mood strikes me, I'll go to a team's roster screen and rank all their players by AVG, HR, OPS, ERA...just to see who the big boys on the teams are. Again, if someone catches my eye, I'll pull up the player and take a look at his history.
Another thing I do that I find fun, is go to the Almanac screen, where you can get a list of all the players in the league, and rank them by possition, just to see who the best catchers, shortstops, etc are.
After regularly doing those things for a season or two, I find that I'm pretty familiar with at least the good players in the league, and some of the more noteable average ones too.