Sam just revealed he's trying to find a good copy of The Sea Fairies to read. Let's give you all a hand to get a copy to read, because 2011 marks the centennial anniversary of the book. So far, there has been no announcement of a special centennial edition, so let's look at our options.
There are two very good editions out there at the moment. Ignore all the print on demand editions. These contain only the text. The two editions out there are by Books of Wonder and Dover Publications. Books of Wonder reprinted both The Sea Fairies and Sky Island in hardcover and paperback, but they dropped the color plates. Dover only publishes paperbacks. I do not own the Dover editions, but their Sea Fairies had the color plates reproduced in grayscale. (Their Sky Island had a color insert. Thanks Eric Gjovaag for the information!)
If you want to get the Dover edition, it can be affordably obtained on Amazon. You may want to pick up their Sky Island, too.
You can try your luck on Abebooks. The Sea Fairies and Sky Island turn up a wide variety of editions, from these paperbacks to Print on Demand editions to antiquarian.
If you're after Books of Wonder, you can look around on Amazon, Abebooks, or eBay, or you can order straight from Books of Wonder themselves:
The Sea Fairies hardcover
The Sea Fairies paperback
Sky Island harcover
Sky Island paperback
Finally, if you just want to read the book and don't mind resorting to digital media, you can do so without spending any money whatsoever.
Project Gutenberg offers a text only version that is available in a variety of formats. Yes, they offer Sky Island as well.
Archive.org has a complete set of scans of the book, complete with color plates. This is also available in a variety of formats. Sadly, there is no similar presentation of Sky Island.
Audio books are available for free online. The people at Uvula Audio are big Baum fans, and offer free audio books of many of his books, including The Sea Fairies and Sky Island. Librivox offers many of Baum's books as audio books. At the time of writing, the Librivox site is having troubles, so here's the Archive.org page of The Sea Fairies audio book, read by Oz fan Judy Bieber. And yes, she's also done Sky Island.
There are other audio books and other sources for the text (including a couple I've set up), but I think these will suit your purposes quite well.
Oh, if you're going to Winkies, better hurry, because The Sea Fairies will be one of the major topics this year, and wouldn't it be nice to know what they're talking about?