I've recently started a fantasy baseball blog, and I use many of those numbers in my assessments here:http://blog.fantasybaseballagent.com
Hardball Times is a great resource, and Hit Tracker also has some great data. I've also downloaded the Lahman database, and manually added some stuff I like to track like ground out vs air outs, etc. I have created some really crazy scatter graphs trying to relate BABIP to factors other than luck.
Yahoo provides easy access to some player splits as well, which comes in handy.
I think the important thing to remember when using these numbers is that there are data points missing in every assessment, and that there are other unmeasurables in play in nearly every scenario. This is why I like to compare BABIP and GO/AO to a players previous history moreso than to other players or even league averages.
Combine the available metrics with reasonable forecasts, available news, and firsthand observations, stir, and often reasonable conclusions can be drawn.
The fun is in determining whether your assessment of a certain player is on or off target, and adjusting for what you learn in the process.
Geez I am a baseball geek...