How can I restore my mobile internet connection? I was tinkering with some settings to try and improve my battery life. I used several settings widgets to turn off some settings, but when I tried to use an app that required a mobile internet connection, it wasn't working anymore.

I looked through all my regular settings (2g vs 3g, roaming etc) and couldn't find what I turned off that's blocking my mobile internet connection.

So what could it be that I turned off?
You may have turned off your APN.  Quick Settings provides the most complete access to settings that I have seen. After you install it you have to customize the view to see all the different options but after you do you'll be able to toggle the APN, Mobile Data, and Airplane mode all separately to isolate which setting isn't allowing you to connect.