I'm sure there is a better place, but if you go to the software download page 0n apple.com and search for iOS Software Updates you can get the basic info for more recent versions.
Apple - Support - Downloads
For a breakdown of security updates you can go to this page.
Apple security updates
Apple does not normally announce or discuss minor updates in advance. Major updates are announced in press events and will be minutely discussed, dissected, and fortified with 8 essential rumors immediately afterword.
To keep up to date on all things Apple it's best to find a source you like and follow it. My suggestions are TUAW, Macworld, AppAdvice, and of course here. You don't' need to follow all of them. There is a lot of duplication. If you don't want to read it all, just keep an eye on the Apple iPad News forum here. You might be a day late getting the scoop, but everything important tends to end up here eventually.