What Makes a Great Ebook Cover?

What makes a great Ebook cover?  I'm in 'cover' mode for my new Ebook coming out shortly and I was wondering if any and all had some thoughts on the subject of Ebook Covers.  It's our first impression before they've read word one.  What makes them great?  What makes you want to read whats underneath?  Leave your thoughts and your covers and let's discuss.

The Best Ebook Marketing Tip you've got?

How does one get into the Kindle 100?  I'm releasing my ebook next month and I was wondering if I could pick your brains on how to market my ebook?  I'm going to blog what works and what doesn't.  So please share your strategy with me and maybe we can find some new ones together.  In appreciation for the help I'll do what I can plug your book as I continue to post.  Alright, so let me have it...