Manybooks has books in different languages already formatted for the Sony Reader:
http://manybooks.net/language.php Their formatting is not as nice as that of Feedbooks, so stick with them for ebooks in French.
The best source by far for ebooks in Spanish is the
Biblioteca Virtual Cervantes, if you don't mind formatting your own texts. They offer classics (public domain titles), but, unlike Project Gutenberg, they are edited and proofread by specialists. Most of their ebooks are in html, so it won't take you long to convert them to Sony's format. If you read Spanish, they also have an extensive list of libraries that offer ebooks in different countries in several languages:
http://www.cervantesvirtual.com/serv...&estadistica=1