To explain web standards we have to mention first that web design isn't just designing a beautiful interface but behind this interface is a structural markup like HTML, XHTML, presentational language like CSS and DOM based scripts like ECMA script.
Of course there are a lot of standards & guidelines stated by the W3C We can mention 3 of the basic standards every web site should follow:
<b> or <i> or using tables for lay-outing, tables should only be used for tabular data like data table or calendar. Every tag should be used for what it is made for only.To make sure if your code is standards compliant or not, use the W3C Markup validator and the W3C CSS validator. To understand more what I mean check this page validity by clicking the XHTML 1.0 and the CSS links.
So does that mean we will have a boring empty interface ?
Not at all as you can see in this site CSS can make beautiful interface designs with all the benefits that we mentioned here, in fact any design can be redesigned with CSS to be standards compliant.
Speaking of CSS beauty we must mention the CSS zen garden project that proves to every body how beautiful is pure CSS layouts. It is one XHTML page and this same page can be changed by only pointing to other CSS file there is over 600 CSS files submitted from designers all over the world. Switch designs from the right panel and be inspired.
A lot of sites make the switch to standards. here is a list of some of the well known switchers :
More redesigners on Eric's redesign watch.