http://www.SeoBook.com is probably my favorite, great signal to noise ratio.

http://www.slightlyshadyseo.com is a less frequent poster, but gives a lot of good gray/black hat stuff that you should at least understand, even if you don't use it.

http://www.seomoz.com is the obvious one, although most of thier content is more beginner oriented.

http://www.sphinn.com is the digg-style seo site, and tends to have about 10% useful content (IMHO).

My best resources are my best competitors :P Just being slightly cheeky here, but in some respects its true. The people who are at the top for the keywords I want to be - you can learn from their sites, how they're built, how they utilise the keywords, who links into them and how its done. This has helped us considerably

yeah http://www.backlinkwatch.com/index.php is a good way of checking out how your competitors build their rankings

The following two sites have provided me with several great nuggets of information regarding SEO

http://www.shoemoney.com/

http://www.seomoz.org/blog

the best advice from shoeomoney was not to worry too much about the indepth SEO stuff - 99% of SEO is keyword research, inbound links, title tag, H1 tag, URL ... the rest doesnt really matter if you are building a valuable service rather than trying to spam google in ultra-competitive keyword areas (travel, finance, electronics etc)

I don't have experience with this myself, but focusing on not sucking seems like the #1 best resource. Perhaps that's slower/too slow though.

Take two web sites/services that don't suck. Add SEO to one and watch the difference. It's staggering.

But, in a way-- you're right. One of the most important things about SEO is links-- which requires you to be worth linking to.

Most of already posted resources are great for learning seo tricks. And the best one for tracking results of your optimization is http://www.semonics.com With this I'm able to track hundreds of keywords.

WebmasterWorld.com by a pretty long shot. I even subscribed for a while. It's the only place I know where the more "silent" SEO people actually spill their techniques every now and then. A lot of the other forums tend to be attention seekers who give good tips but they're keeping most of the gold for themselves.

A searchable directory of resources serious webmasters need for their day to day web mastering, with emphasis on quality and usefulness. =========== Kyle http://www.widecircles.co

In addition to the standard ones mentioned below (seobook, seomoz etc) - you should go check out bluehatseo.com wolf-howl.com stuntdubl.com http://www.jimboykin.com/index.php

http://www.mattcutts.com/blog/ is good to watch

you should use this: http://www.google.com/webmasters/tools/

http://forums.digitalpoint.com are ok.

Are there any good SEO forums that are free? Or any that are worth paying for?

This is good free tool http://webceo.cbarker.ws/

My old boss swore by the guy at seofaststart.com

I read the ebook (free) and it seems straight forward enough.