I would only go on the places that I do the best selling my ebooks and that is Clickbank and the Kindle. It just depends on the ebook you are selling and whether or not you want affiliates promoting it.
The first thing I'd do is get it on Amazon. That earns you instant credibility. You can drive traffic using Adwords. But if you want to make some real cash, get it up on Clickbank or JVZoo. Like Greg said above, you need some killer copy. What that means is... You need copy that effectively triggers the emotions that connect with your prospect's current circumstances... ...and leads them to what they want. If your ebook can accomplish that, then your front end copy can describe some pretty hot benefits. The question is: What kind of quality does your ebook contain, how does it compare to what your competition is putting out and will it actually HELP people change their lives in some way? If you REALLY can HELP your prospects, your sales letter and/or VSL has to fully communicate HOW and WHY. You need a brand, hook, USP and call-to-action that ALL sizzle. Hope that helps. marc