Ivan Goldberg is a well-known psychopharmacologist. He writes regularly on various mailing lists and newsgroups. Collected writings of Ivan Goldberg is a searchable collection of pieces of text he has written on the Walkers-in-darkness mailing list. If you don't find anything, see the index of precollected keywords.
Some mixed smaller resource are also available. You may want to check two scales to measure depression and mania. These are not for self-diagnosis. Instead, you can follow your development, or just read the questionairies to improve your insight into typical symptoms.
Winter Depression (Seasonal Affective Disorder [SAD]) information provided by Forrest Toft contains quotes, pointers and information on where to get light sources. More hard-core information about SAD and light therapy is also available, quoting clinicians specialized on SAD.
Finally, if you are hopeless, read about John Nash.
Pendulum Resources on bipolar affective disorders look promising. They nicely fill the "bipolar hole" of this server (or, alternatively, this server fills the unipolar gap :) ). OCD (Obsessive-Compulsive Disorder) server is massive. Mark, Kelly, and Susan... they have got the med info. Eli Lilly has a WWW server, but I'm somewhat pessimistic about depression-related articles to appear there. They invented Prozac, and fluoxetine general as well, if you didn't know. HabitSmart deals with addictions.
Practical Psychology Magazine (PPM) - visually nice, contains popular articles written by professionals. I haven't had time to read anything, but this seems entertaining to say the least.