Ditto what Jan in Ca said: RAVELRY!
Also, great pdf patterns (not free, but reasonably priced) are found at Twist Collective.
It's a favorite haunt of mine.
I am totally into PDF patterns. I do subscribe to Knitters, Interweave Knits and Vogue Knitting...however, I don't know why. Not for patterns. I think I love reading through the magazines, keeping up with what's current and fresh in the knitting world. I love the ads. I recently purchased a knitting bowl based on an ad I saw in the current Vogue Knitting!
I agree, Knitty
is fantastic, as well as KnittingPatternsCentral
You can spend a fortune at Barnes and Noble on knitting books...and Amazon...and KnitPicks...but that's a dangerous road...
I think as far as books go (for sweaters, that is)....I've been happiest with Classic Elite soft cover booklets. Almost 100% of the patterns are genuinely wearable and knittable.