In the world of SEO things change on a daily basis and part of being a good SEO yourself means knowing what these changes are and even predicting how they will affect traffic coming to the sites you look after. Bear in mind however that the constant changes in the search engines are for the most part inconsequential and you need to use your own judgement to make a call on what changes will have a noticeable impact on what you do as an SEO.
But it is not only the changes in the search engines that you will want to keep up to date with. There is a tremendous amount of very intelligent people working in the SEO industry who are happy to share their views and understanding with you. The smartest people in the industry however are those that realise they don’t yet fully understand all that SEO is and test every theory or assumption that they make.
Finally there are those that take the next step and put their ideas and testing into practise, taking the form of a nifty web based tool. The more data points and tools you can use for analysing those data points the better you are going to get at understanding SEO.
Here are the blogs that I personally use to stay up to date on what is going on in the SEO community:

1. SEOmoz Blog – Starting with the big boys SEOmoz is a daily SEO blog providing you with some of the latest news along with some great tools and concepts in the SEO industry. The thing I most like about SEOmoz is they will test their theories, supply you with their findings but also give you the same data for you to make your own conclusions from. As you can imagine this is a very effective way to learn the art of SEO. You will also find many people contributing to the site via their YOUmoz section with the best articles being promoted to their main blog ensuring you always get a fresh mix of new ideas and techniques.

2. Viper Chill – Viper Chill is the viral marketing blog of internet marketer Glen Allsopp. I have to say that this is one of my favourite. The posts unlike some other sites are much longer and talk you through a complete concept or methodology from beginning to end. Equally impressive is the effort that Glen puts into answering comments, so if you do find yourself struggling on a few points don’t hesitate to post a comment. Since the re-launch of the Viper Chill website in October 2009 Glen has published a monthly report, up until September 2010, offering a unique insight into how to create a popular and successful blog… definitely worth a read if you have not visited the Viper Chill site before.

3. SEO Book – Another of the big SEO blogs SEO Book produces a number of articles that will question as well as reinforce why you or anyone should practise SEO. More informative than action based SEO Book is a good blog to read if you want to increase you understanding on some of the inner workings of the search engines.

4. Distilled Blog – Distilled is a UK based SEO company that also operates in Seattle and has connections to SEOmoz. Blog posts are less frequent than the SEOmoz blog, which isn’t a bad thing at all, and often introduce you to some nice new tools or plugins for you browsers.

5. Google Webmaster Central Blog – No inside secrets or ground breaking techniques to be found here but the Google Webmaster Central Blog will keep you up to date with any changes Google think are important, which most times makes them important.

6. SEO Blog by Dave Naylor – This is a great blog for getting the latest on those little changes that Google makes on a continual basis. The blog will lay out the exact changes that have been spotted, usually with a nice screenshot, along with the author’s opinion and what it could mean for us SEOs. However you are encouraged to make your own mind up and ultimately that’s the way it should be and where this blog succeeds.
Wildcards:

7. Blue Hat SEO – This blog unfortunately hasn’t had a new post since July 2010 but on the plus side definitely won’t clog up your feed reader! What you will get however if you take a look at some of the past posts is a completely different view on how to do SEO. It is always good to read a few blogs like these that push the boundaries of what is considered “ethical” SEO. Learning how to build your SEO Empire is something that will surely get you hooked not only on this blog but a whole new way of looking at the SEO world.

8. SEO by the Sea – If keeping up to date on the patent filings of the world’s biggest search engines is your thing then Bill Slawski of SEO by the Sea is your man. Why I stopped reading this blog; There is some great retrospective insight to be found here however from my limited understanding it seems most of these patents take a minimum of one year to be granted. Personally that’s a little too long in the SEO industry for my liking. I would however recommend this blog for anyone wanting to better understand the way Google and other search engines work at a very granular level. The feeling I get though is that the time will also come when you decide what happened several years ago isn’t a great deal of help.
Update: It seems I may have jumped the gun when claiming that information from SEO by the Sea is only useful for retrospective analysis. Thanks to Bill for his informative points in the comment section at the end of this article. It seems that some of the patent filings are published before the technology they protect has been implemented and therefore could provide valuable insight into the future of the search engines.
Of course you can never be sure how long it will be until these technologies will be implemented if at all. However there is value to be taken from understanding the direction and thought process that is being taken by the major search engine providers. Therefore I will update my verdict to say that there is some valuable insight to be gained from SEO by the Sea. Although you should bear in mind that the technology discussed may have been active for years, due to be implemented in the near/distant future or may never by used by the search engines. A key point that Bill does make though is that this information is provided directly from the search engines something that, as mentioned above, will help you learn from the primary source you are optimising for.
I have found that other blogs such as Search Engine Roundtable and Search Engine Land produce far too much content on minor issues that just creates noise for you to sift through. Although it is only right that I mention them here, as these blogs are well thought of and often referenced sources of information within the SEO industry.
Finally to truly stay on the pulse when it comes to developments in the world of SEO you need to be able to find information on subjects that might not have filtered through to the top SEO blogs. For this Twitter is your greatest ally. Start by following these guys and you will soon have a fresh stream of high quality SEO related news and tactics from across the web:
@Seosmarty – Ann Smarty is an avid guest blogger with her own guest blogging community; MyBlogGuest.com which you can join.
@rustybrick – Barry Schwartz as founder of Search Engine Roundtable delivers some great links to articles on the site. As mentioned above Search Engine Roundtable is one of the sites that pumps out a great deal of content. Using Twitter provides an efficient way to filter this explosion of content for news and information that interests you.
You can also follow me here 
P.S. I should also mention Sphinn, the SEO equivalent of what Digg used to be, is a great way to find the current top articles and information as decided by the SEO (Sphinn) community.