Nausicaa.net: Laputa Castle in the Sky
Nausicaa.net is the best reference site for Studio Ghibli films. In its Laputa page you can find an illustrated synopsis, the always fascinating FAQ, scripts, lyrics, etc. Be sure to visit the section dedicated to diary and interview excerpts with Joe Hisaishi concerning the new soundtrack he created for the Disney release "Castle in the Sky".
Buta-Connection: Laputa, le château dans le ciel [French]
This site is really good and I think it offers really interesting information. Aside from finding a very detailed illustrated synopsis and character profiles, it has other sections like a 2 page analysis of the film, a page detailing the film origins and a section dedicated to art technique of the film. In addition, there is a section dedicated to the book Gulliver's Travel. I like this site a lot and I hope you will too. The link I posted above takes you directly to the Laputa site, but as a result it eliminates the frames that suppose to be part of the page; you can enter through the main page at http://www.buta-connection.net.
Not just a fanlisting. The site also features very good information about the film, including character pages, reviews, collections gallery, etc.
Levistone.com - Laputa
Wow, until I started reviewing the links again to write this page, I had forgotten how much was offered on this website. This is another very fan-friendly website. Once known as the "Laputa Website in Hong Kong" the site has undergone a design change and new additions (I think). One of the things it has that I haven't seen anywhere else are Laputa piano scores. The main emphasis on the web is on the art of the movie, there are three separate sections including watercolour images, screen captures and high quality images.
Carrot's Laputa site [Chinese]
Carrot has created a wonderful Laputa information site with character profiles, along with CD and book information. What I especially like most about Carrot's page is her collection of Laputa watercolour artwork.
Comparison of Nadia and Laputa
This site provides an illustrated comparison of Laputa Castle in the Sky with another the anime series Nadia. There are indeed a lot of similarities between the two films. While this site will be of special interest to those who have seen both of them, but I think people who have never seen Nadia (like myself) will enjoy it as well.
Mazda Japan has a car named "Laputa". It is a compact/mini wagon car that to me is like a combination of the recent Toyota Echo and the Honda Civic Wagon from the late '80s (*note: my knowledge of cars is limited). Judge for yourself by visiting the link above.