I have been a long time fan of SitePoint.com for their fantastic web design and CSS articles. I found myself, more often than not, being directed to Sitepoint.com through my Google results when searching for answers on CSS and web design problems.
I came across this ebook series, that SitePoint has created, called The SEO Business Guide. A friend of mine had recommended it to me so I checked it out. You can even get a few chapters of the book for free. From what I read it was a worth while read. SEO is very important to any web designer these days, if you want a good starting point, have a look at SitePoints SEO guide book.