Of Mice and Mayhem is a heavily involved Rescue Rangers fanfic. The art is superb, and the plot and writing are achingly campy — which is really half the fun. Have a fast net connection and lots of time; it’s over 200 pages long, and the JPEG filenames vary for each page to avoid automated hot linking. It’s especially appealing to my inner seventh-grader — the one with an enormous Gadget crush.
Link found via this MeFi thread, from which we find the Brunching Geek Hierarchy. Back in my role playing days, I probably would have been somewhere near the bottom of that chart, since I did write Trek-based furry fanfics. Featuring a Gadget-like character. (No, seriously. Just ask Antifaust. He still has the Wordstar files of my Next Generation novel about the psychic mutant rat.)