ISBN?

If you get your own ISBN the book is not tied solely to Createspace.

Remember that you need a new ISBN for every format. One for .pub, one for .mobi, one for paperback, etc.

If you want to set yourself up as the publisher, you wouldn't be able to use their free ISBN. But doing that also requires some other work on your end, such as setting up a sole proprietorship or something similar (I'm not one for legal advice, but I researched this myself when I was getting ready to publish and decided it was too much trouble for my purposes.).

If you don't plan on setting up your own publishing company, then the free ISBN should be fine. It's what I used, and I'm happy with it. It only applies to the paperback edition of the book, which CS prints, so I don't really mind that CreateSpace shows as publisher of record. Some people don't like that, so spending the extra $10 to be able to put their own name or company as publisher is worth it.

As for the 3rd option, that ISBN would be yours completely, with no tie to CS. If you think you might later want to move your book to another POD, with this option, you would be able to keep the ISBN with it and sell it anywhere you'd like. (Someone correct me if I'm wrong, but this is the way I understood it when I was researching. I could be wrong, though!)

If you're going to also put out your book in ebook formats (Kindle, ePub, etc.), then as mentioned earlier, you will need a different ISBN for each. Smashwords has them free if you publish through their service, and Kindle and Nook don't require them - they have their own identifiers that they also offer free if you choose to publish to them directly rather than through SW.

Good luck with your book! I have to admit, I found that ISBNs were probably one of the more confusing aspects of self-publishing, so I hope I was able to shed a little light.

I wrote a guest post on Reena Jacobs blog about this earlier this year.

Here's the link: http://reenajacobs.com/blog/2011/03/guest-post-v-j-chambers-on-the-importance-of-isbns/

All of that, however, is just MY opinion. Your mileage may vary.