Over the years, the Baseball-Reference.com site has been an invaluable reference source, not only for players' major and minor league statistics, but for team-and-year information such as defensive line-ups and batting orders for each game, transactions, minor-league affiliations, and many others.
A few years ago, I also discovered a Retrosheet link at the bottom of each player's page. There, one can find out the player's statistics for each game played, including whether or not he started, and what position was played (including PH and PR).
One of the features I like on the Baseball-Reference home page is the group of player
thumbnails (sample below). I like to guess who the players are, before
hovering my mouse pointer over them to get the names. (I usually have no
shot at the older black-and-white photos, but can name many of the
late-1960s players on sight.)
I saved this grouping a few months ago, in anticipation of a post like this one today.
Top row: Mike McCormick, unknown, Johnny Callison, unknown, Ken Boyer (or is it Curt Simmons?), unknown.
Bottom row: Johnny Romano, unknown, unknown, unknown (maybe Dick Radatz?), Bill Monbouquette, John Roseboro.
Surprisingly, I've noticed that there are never any players from the 1970s and beyond included in the photo grids.