The ebook formatting service I settled on is called Ebook Formatters. I'll tell you about them, then offer a second name I also recommend strongly but which I couldn't use for this book because of scheduling conflicts on both sides.
First up, the awesome Casey Babylon. For a book of under 100,000 words, Casey charges $25 to format for Kindle or Nook. She requires prepayment, by PenPal only. And she pledges to stay with her clients until they are satisfied. The initial turnaround is surprisingly quick: 24 hours. In a ms. of 44,000 words, I found only three very small issues arising at their end: e.g., a space omitted between a chapter number and the text beneath. Though I'd proofed the manuscript throroughly, I found two slipups on my part: A missing opening quotation mark and a single typo. All of these issues were addressed immediately.
Where Casey really rocked for me was in her willingness to check small discrepancies between her formatted Word doc and the Kindle preview screen: e.g., lines of dialogue that looked indented by a couple of extra spaces and didn't 'wrap' on the preview page. Casey explained that different viewing devices yield different displays on occasion, but that--as long as the Word doc was accurate--all would be well in the Kindle ebook final form. Still, she agreed to go through a detailed list and double-check each item.
She's courteous, he's fast, and she likes helping writers get their books into dream shape.
Also recommended: Lucinda Campbell at design.lkcampbell.com. Lucinda's in the same price range as Casey, but booked for a couple of weeks in advance. That said, I was blown away by the first email from her--in which she advised me to try resaving my troubled ms. as a HOTML document before I spent a penny. For the record, this solved about 80% of my formatting problems.
Contact both and decide for yourself if you'd like to spend 25 bucks to save yourself a world of formatting woes.