Information/General Pages:
-Mahou Tsukai TAI! - I am proud to say that I learned this wonderful series existed through this website, and it's what got me hooked. It's got a basic summary of the plot and brief character summaries along with a few images of each character, product info, and info on the TV series.
-Mahou Tsukai Tai - This is another one of Hitoshi Doi-san's anime websites (he's got like 50 doesn't he? @_o). It's really good for info about the CD's/LD's and who plays the voice of each character.
-Magic User's Club (Mahou Tsukai Tai) - A very brief all-around page with character info, images, and a fanfic.
-The Magic Box - a small but interesting little site. Has fanart, "Mahou fun", and brief character profiles. No longer being updated, unfortunately ^^;
-Never Stand too Close to a Naked Magician - A well rounded site, with summaries, characters, fanfiction, and an Aburatsubo shrine/club. Doesn't seem to have been updated in a while, though ^_^;
-Mahou Tsukai Tai :: Archen's Anime Page - A portion of a larger anime site focusing on MTT. Informative site with a nice layout and such. I like the underwear section ^_~
-My Mahoutsukai tai shrine - a page with some charater profiles and a few images
-Animeinfo.net: MTT - an easy to navigate page with information, doujinshi, clips, etc (new link)
-OUA Presents: Maho Tsukai Tai! - if you can't find what you want here, it's probably up on this site :) Merchandise info, series info, image galleries, etc (new link)

Image Galleries:
-The Amber Anime Archive's Mahou Tsukai Tai! - And old but reliable image gallery, it's got scans of the LD's and the CD's, two songs in MP2 format, and a pencilboard scan. I finally got the URL right :)
-Page 1 (at Shoujo.com) - Another really great image gallery! This one's got pictures from what I assume is an artbook or something ^^ (this site seems to be down right now. Hopefully it's coming back up ;_;)
-Where all little bears come to play - a cute site with GREAT scans from the manga and the postcard set. Very nice ^^ (this site has vanished, apparently. If anyone knows if it has a new URL, please let me know!)
-Snake's Anime Archive: Mahou Tsukai Tai - Has collage type scans and scans of MTT trading cards :)
-Hyel's Tiny Little Mahou Tsukai Tai Gallery - a small gallery of scans, as the title says. However, several of these are from the manga, which makes it stand out

Character Shrines:
-ecchi yo! Takakura webshrine - okay, dude, I have obviously not been surfing the web NEARLY enough. Someone made a Takeo-shrine. Go, see, worship ^_^
-Gomen! - a cute looking Sae shrine, with info and images and such. Heh, love the title *grin*

Other:
-The Mahou Tsukai Tai! Webring - someone had to go and start one eventually ^_- A webring for mahou pages and it also hosts a MTT! Mailing list.
-The Unofficial Mahoutsukai Tai book of spells - a listing of all the spells used in the OAVs and what they do
-MTT-TV Mailing List - what it says. A yahoogroups based mailing list about MTT