Power of Now is definitely worth a read, but I agree with the comments about it's slide towards New Age territory.

I think 'Feel The Fear & Do It Anyway' is also worth checking out.
It's quite simple and succinct, but easy to digest and lots of really useful practical take-outs to get you through some tough spots and laying the foundations for strong inner game.

Also obvious but worth reiterating, don't beat yourself up for having the days where you aren't quite rocking the vibe - everyone does, perfectly normal!