I work as a freelance copyeditor and have a lot of self-published authors as clients(several write books dealing with tax/finance/business issues that I won't mention here.)
There are three titles I can recommend:
For fiction, Belinda Kroll's "Haunting Miss Trentwood," which she calls a "quirky historical romance."
http://www.amazon.com/Haunting-Miss-Trentwood-ebook/dp/B0047GMI9Y/ref=sr_1_cc_1?ie=UTF8&qid=1306633945&sr=1-1-catcorr Belinda never queried any agents or editors--she's completely committed to being an "indie" author, largely because she wants complete control over the publishing process. I've found this is often the case with serious self-publishers--there's a real community of authors who have no interest in traditional publishers and who support one another strongly. Belinda has a master's in computer design so she's very knowledgeable about certain aspects of self-publishing, such as interior formatting.
A non-fiction book that I love is called "Lesson Plans Ahoy!: Hands-on Learning for Sailing Children and Home Schooling Sailors" by Nadine Slavinski,
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=lesson+plans+ahoy&x=0&y=0 Nadine has a PhD in education from Harvard and spent a year sailing around the world while educating her own child. This is a great example of a niche book that's too narrow for traditional publishers, but has been very successful among that homeschooling segment of the population. She's writing another version that will supplement homeschooling on land. The lessons are so well done that I'm using them for summer enrichment for my daughter.
Finally, another book that's probably too narrow for a traditional publisher but is really nicely done (and I believe has done well in sales too) is called "Mommy, Draw Stars on My Tummy: Rhymes, Songs and Touch-Play Activities to Stay Connected" by Martine Groeneveld.
http://www.amazon.com/Mommy-Rhymes-Touch-Play-Activities-Connected/dp/0982295901/ref=ntt_at_ep_dpi_1(And just a note: If there are clients reading this that I didn't mention, please don't be offended. I'm just trying to give examples of self-published titles that I think are very solid, but it doesn't mean yours isn't!)