Baseball Musings has a lot of interesting things. My favorite is the day-by-day database because it allows you to sort data by any dates you want. For example, you can get the splits for a hitter from July 22, 2011 through April 29, 2012.
The Vintage Panoramic Pictures thread at Baseball Fever is my favorite source for photos of ballparks, teams and players going way back. Countless unbelievable shots. The focus is on panorama type photos of ballparks and teams, but many others too. A bit hard to navigate at first, but once you figure it out it is well worth the time. Many are captioned with many old team photos having the player names. Many St. Louis teams included, and not just the Cards and Browns. Quite a while back on The Cardinal Nation Blog I linked to a photo of the 1899 Perfectos with Cy Young.
I previously mentioned www.firstinning.com as a decent place to go for some minor league splits, like month-by-month batted ball data ... LD%, GB%, FB%, stuff like that. This website appears to be gone now. Not sure if it moved or is just a goner. Baseball Reference now has some of the info I used to get on First Inning.
They've got a really nice Splits Analysis tool that I like to use. Although the owner said a few weeks ago that they probably won't be updating stats in-season so that they can focus on site development and historical data.