Warner Bros. Cartoons Filmography And Title Card Gallery - Can't begin to tell you how grateful I am for this site. It saves me the trouble of typing out the credits! :D
Although the Spumco site is down you can take a look at its archived pages at the "Internet Wayback Machine". The cartoon magazine, a huge influence on me, is definately worth reading. The stuff that requires flash doesn't work (So no George Liquor or WPH :( ), but you can still look at the comics and things. :P
Cartoon Brew - Amid Amidi and Jerry Beck (of the two sites below), and others blog.
Animation Blast - My favorite animation magazine (out of all the hundreds of thousands of high quality animation magazines sitting on the rack at Walden...oh wait there are none) with lots of fascinating commentaries.
Cartoon Research - A grabbag of cartoon-related stuff, from reviews to screenings to original titles to other assorted crud, plus it's run by the guy who gave us The Golden Age of Looney Tunes and The Compleat Tex Avery (my hero).
Spumco Ren and Stimpy archive - It's a very biased and inflammatory take on the Spumco/Nickelodeon debacle, but it's essentially true. Check out the episode guide and drawings while you're at it. I do owe this site a debt of thanks as it's where I first learned of Man's Best Friend, but it will probably never be updated again. :(
Definitive First and Second Ren and Stimpy episode guide by Michelle-Klien-Haas, very helpful for the Ren and Stimpy reviews.
Keith Jones has a site devoted to Cow and Chicken, with some insights on cartoons in general.
Mike MacKenzie (aka Whiggles) - Several great Ren and Stimpy reviews on here, as well as DVD movies.
THE ULTIMATE LINKS PAGE - If you like rock music, check out these review sites, although the guy forgot to link to his own page.
Comic Related
Steve's Reads: Steve Bolhafner's site introduced me to a lot of the comics that drastically altered my perception of the medium.
Savant Mag - Comics reviews and activism and stuff.
CBR: I read it mainly for commentaries, not news.
Beek's Book Reviews - Good review site for comics.
Artbomb - Another comic review site.
Popimage - Another good review site for comics.