If you work in search engine optimization, or Internet marketing and you haven't been exposed to Drupal yet, it's a wonderful CMS for a variety of applications. Specific to this blog post, however, Drupal is a phenomenal platform for search engine optimization and Internet marketing. With the right modules installed and configured, Drupal can be a complete joy to work with for an SEO. Use the following as a guide for the best Drupal SEO and SEM modules to install for your website.

• Page Titles
  The Page Title module allows you to specify a different tag from your content page title (typically the H1).
• Path (core)
  In Drupal 6.x, Path is a core module, which means it's already included in the basic Drupal download. Path allows you rename Drupal's default URLs and combined with Clean URLs (also in core), you can create keyword rich URL strings for your interior pages. For a good example, look at the URL for this blog post.
• Path Auto
  Combined with Path, Clean URLs and Tokens, Path Auto lets you specify default URL settings. For example, it's possible to set the URL string to be the same as the content page title (the h1).
• Blog (core)
  Think of a blog as your website's SEO engine, where the fuel is original content. Your blog will build user engagement, keep the spiders crawling your site, and bring in some long tail search traffic, among many other benefits.
• Google Analytics
  This one's obvious. You can't do a good job if you're not tracking your site. This module automatically generates the Google Analytics tracking code, all you have to supply is the account number (typically starts with "UA-").
• XML Sitemaps
  This module isn't quite ready for Drupal 6.x yet, but when it's finished, it's a must have module for your website. XML Sitemaps generates a standards compliant sitemap for your website and with the right configuration, submits it to all the major search engines automatically. Experiments have shown that with a sitemap submission, search engine spiders will index your site more often, and faster.
• Global Redirect
  Global Redirect makes it easier to generate auto 301s and a host of other URL and redirect applications.
• CCK
  Like the blog module, CCK is another atypical addition to a Drupal SEO module list. CCK allows you to create custom content types with custom input fields. For example, if you ran a music review site, you could create content types for artists and albums, with each having different input fields. Where this helps with SEO, is that with the right input fields defined, it can be easier to capture long tail search traffic. In the music review example, you could add input fields on the album content type for cover art, year produced, track listings, etc.
• Filter (core)
  The Filter module allows you to specify custom input filters. These input filters can do anything from stripping out dis-allowed HTML tags, to automatically adding the rel=nofollow tag to links. This is useful especially in community websites or user driven websites.
• Taxonomy (core)
  As far as SEO is concerned, the Taxonomy module allows you to create a free tagging and categorical organization system for your website, while substantially increasing you sites page count. Each new tag or category creates it's own organization page for other content that's been tagged similarly.
• More Like This
  More Like This improves user engagement (and theoretically time on site and bounce rate) by adding a block of related content to specified content areas on your website.
• Add This
  Add This makes it easy for you and your websites users to promote your sites content over various social networks.
• Captcha/Mollom
  For SEO, controlling spam and spammy behavior is a major consideration for your website, and is one of the few places where you can practice "preventative SEO". If your site gets hacked or too heavily spammed, it can be penalized by the search engines. Both services help control spam, my preference lies with Mollom, but choose the service that fits you best.