There is an incredible amount of usable opening analysis available free on the web, so that many club and online players these days likely never buy chess books but rely completely on what they can find online. Here are a few good resources for accessing chess opening analysis:
Chess Opening Links
I have been planning to update my links to opening analysis, because I noticed recently that it has accumulated quite a few broken links and I know there is lots of new stuff to add since my last update (including practically everything I've written at my blog!) Unfortunately, I did not think to organize my listings by ECO codes, which would have made it much easier to use (especially those not familiar with the English names for the openings they like.) It is still a very good resource.
World Chess Links: Theory
Follow the links on the left to navigate to either general resources or links to specific opening lines, by ECO categories and common names. Then be sure to use the page buttons to access everything. This is a very strong and deep site with more information than my own. It is relatively new (less than a year old), so most of the links are fresh and good.
Described as a directory or a database of opening analysis links, this seems a very promising site, only recently re-opened. They also publishe some original analysis, including an excellent and detailed article on the Alekhine's Defense, Two Pawns Attack.
The Chess Portal (Schackporalen): Chess Theory: Specific Openings
One of the better links collections, but like my own rather out of date. Written in multiple languages.
I think my own site is more up to date than this one, which means it is very out of date indeed.
MECCA - CLINK! - Click the link - Theory: Openings
This one also seems a bit out of date, but it does offer lots of links.