There are, as one might expect, many sites in Japan devoted to Maison Ikkoku, and to the works of Rumiko Takahashi in general.
Perhaps the best of the Maison Ikkoku sites is the one maintained by Asuka Kyouka. Of course, it's all in Japanese, but there are lots of images that should be of interest to the serious fan, even if he/she does not understand a word of Japanese. Here is a brief tour guide.
From 1980 to 1983 (that is to say, during the first three years of publication of Maison Ikkoku) Rumiko Takahashi lived in a district of Tokyo called "Higashi-kurume." This neighborhood provided her with the inspiration for many of the locales depicted in Maison Ikkoku (in the imaginary district of "Clock Hill," where the story is set).
Asuka-san spent some time wandering around the neighborhood and taking pictures, and then putting together the pictures with the corresponding scenes in the manga. The result is fascinating, to say the least. There are four pages of images, including one with a clickable map. (The others are here, here, and here.) There's some overlap between the various pages, but you should visit them all, and click on the small pictures to see the larger image and, in most cases, the corresponding image from the manga. It's definitely worth the trip.
Unfortunately this list only goes up to episode 59 so far, but this is your chance (possibly your only chance ever) to see the images of the original first pages of those early episodes, including many in color! Too bad the images are so small...
This will not be so useful unless you can read some Japanese, but it is kept quite up to date, has comments on all the works, and also the occasional rare color image if you follow the links.
Most of the original episodes' titles involved puns or wordplay of some sort, and somebody in Japan has compiled a list explaining every one. Since the English edition has seldom kept the original titles, I have made limited use of this list (the existence of a similar effort in the English Guidebook, in file guide-r8b, should also be noted). Fans who are learning Japanese and/or have the original manga should find the Japanese list very interesting, however.
And finally...
For all your Takahashi news, partly in English, too!