Popknits
One of my favorite knitting magazines, this free online mag is all about vintage-inspired designs. A must for anyone who loves vintage fashion, as well as other fashion-loving knitters (the patterns may be vintage-flavored but are decidedly modern at the same time). Make sure to browse around their archives as well so you won't miss anything pretty.
Knotions Magazine
Great online magazine for knitters. Knotions has a wealth of wonderful free patterns and articles for knitters to enjoy and of course knit.
Knit on the Net
Another fantastic online knitting magazine with heaps of pretty free patterns, and stunning photography to boot. Check out their archives as well, there are some great free patterns to be found there.
Ravelry
Online community for knitters and crocheters with many useful as well as fun features. A great place to socialize with other knitters, admire finished projects and list your own FOs and WIPs, as well as keep an overview of your yarn stash. Ravelry requires you to apply for (free) membership, which is usually granted in a day or two.
Yarndex
A detailed listing of most of the more famous yarns available, including information on discontinued yarns and colorways. The yarndex lists all of the yarn's information, including the content, yardage and weight, making it an invaluable research tool when substituting yarns for a particular pattern.
The Inside Loop
The Inside Loop is an online magazine dedicated to fibre arts in the U.K. It is currently on hiatus, but there are still some very nice free patterns to be found in the archives, as well as articles and other features.
YarnStandards.com
Standards and guidelines for knitting and crochet, including abbreviations and sizing/standard body measurements.
Knitting Pattern Central
Large directory of free knitting patterns, plus loads of other information.
School House Press
The knitting publishing house that was launched and made big by none other than Elizabeth Zimmerman. It is now run by her daughter, Meg Swansen and all of Elizabeth's books are in their catalogue.
Vogue Knitting Stitch Library
This part of the Vogue Knitting website lists some fantastic stitch patterns. They are sure to inspire designers and knitters alike!