Here you can find places to download manga for free.
http://www.redmadness.net/ ---> Original manga
http://www.narutofan.com/index.php ---> Naruto
http://www.geocities.com/hellsing2006/hsm.html ---> HELLSING (only up to number 5)
http://groups.msn.com/ATU-BOTI/maturehellsing.msnw ---> Renka, Ghost in the Shell, Wolf's rain, Blood the last Vampire 2000, Great teacher Onizuka, HELLSING, Peace Maker, Peace Maker Kurogane, Chrno Crusade, Neon Genesis Evangelion, Wolverine: Snikt!, Blade of the immortal
http://tidwah.net/ ---> Lots, and I mena LOTS of free mangas.
http://mangatranslation.com/vgd/ ---> Vulgar Ghost Daydream (download by bitorrent, up to volume 7)
http://mypage.bluewin.ch/squigglemanga/ http://www.manganews.net/ ---> Too many to list, but it includes, by example, Sailor V manga
http://www.dailymanga.org/ ---> Same here.
http://www.akatsukimanga.com/download.php ---> Black Lagoon, Ichigo Mashimaro, Pretty Face, Orefeti, Naisho no Tsubomi
http://pages.sbcglobal.net/tenshi/sdindex.html ---> Slam Dunk
http://www.omanga.net/ ---> Too long to list, but many famous works
http://www.mangadownload.net/manga.php ---> Biggest archieve to download manga I've ever seen O_O
http://www.stoptazmo.com/full_metal_alchemist/ ---> FULLMETAL ALCHEMIST
http://www.stoptazmo.com/ ---> Many mangas :P
http://www.theotherside.amorous-socialite.net/ --> download understream manga
http://zephyrfalcon.org/links/manga.html --- FOLLOW THE ARROW