Anyone know of a good app that changes the default lock screen?

Screen Mode Widget Lite (and install as a single-icon widget). Cycles through three modes, so If I'm just at home I turn off the "screen lock", but turn it on if I'm out and about with the phone in my pocket.

On a related note, I also recommend the Quiet Time app, which is excellent for setting "downtime" when you go into a meeting etc, with a timer function and various options.

These two sit at the top of my primary Home Screen and are invaluable