JoJo's Bizarre Copypasta on how/where to read. Araki Compilation Mediafire with all of Jojo and other Araki works:

Parts 1-3 are on or here: Part 1 - Phantom Blood

Part 2 - Battle Tendency

Part 3 has an official English release from Viz, if you don't like the scans, buy that, or slap the text onto better raws yourself!

Part 3 - Stardust Crusaders

Part 4's translation is just bad(and wonderful), it's being redone(slowly) here: You'll have to stick with the wonderful Duwang edition for the parts that haven't been redone yet.

Part 4 - Diamond is Unbreakable

Part 5 is also on mangatraders. About it's translation, it's pretty bad, just more gramatically correct than part 4's, so it doesn't seem as bad. JoJoProject is starting to retranslate/scan it. Redone volumes will be with the 6 and 7 scanlations.

Part 5 - Golden Wind

Parts 6 and 7 are here: Status updates on Part 7, so you don't have to scream SCANS WHERE all the time: