You can create your own online library catalog (private or public as you wish). Finding and adding books is *insanely* easy. The interface is smooth and lovely. You can add your first 100 books for free, then it's $10 for a year and $25 lifetime.... I sense $25 is going to be floating out of my wallet very very soon.
You can see my catalog here - just the books I can see from where I'm sitting :)