Ab Exercises/Getting that 6-pack

[ctv1116]

I've been trying to strengthen my abs to help correct the lower back pain I've been having (OK, I admit it, I just wanna have a sweet 6-pack). I only have a small layer of fat in my stomach area, which of course I will need to have to burn off. Otherwise, I was wondering what exercises are optimal for strengthening the abs. I've been doing the first few exercises on this list to get myself going. A couple questions:

1. Are these the best ab exercises?

2. Do you need rest days between ab exercises like working with your arms, chest etc., or is this an endurance thing where you can do it pretty much every day?