Admitedly, this is an ambitious list, but it's also a worthwhile one. Below, I've attempted to lay the foundation for every piece of website data available to marketers, researchers and the curious. Competitive analysis experts, welcome to data paradise:

Technical Data

• IP Address - via DomainTools Search
  (e.g. SEOmoz - 204.15.225.178)
• Other Sites on an IP Address - via IP Query at Live.com
  (e.g. SEOmoz's - 204.15.225.178)
• Server Type - via DomainTools Search
  (e.g. SEOmoz - Apache)
• Response Time - via DomainTools Search
  (e.g. SEOmoz - 5.78ms)
• Name Server - via DomainTools Search
  (e.g. SEOmoz - dns1.dedicatedns.com)
• W3C Validation - via W3C Markup Validator
  (e.g. SEOmoz - we passed!)
• CSS Validation - via W3C CSS Validator
  (e.g. SEOmoz - validates)
• Speed Report - via WebsiteOptimization.com
  (e.g. SEOmoz, 23.44 seconds @ 56K - sadly, you can't link directly to these)
• Use of Text - via Ranks.nl KW Density Checker
  (e.g. SEOmoz's homepage has 662 total words, 336 uniques and "seo" is the most common, again you can't link directly to these pages; note - I'm not endorsing KW Density; I just appreciate their tool)
• HTTP Headers Response - via Web Sniffer
  (e.g. SEOmoz - 200 OK)
  

Ownership/Hosting Data

• Whois Data (registrant, registration date, contacts, etc.) - via DomainTools Search
  (e.g. SEOmoz)
• Additional Sites Owned/Registered - via DomainTools Search and Alexa
  (e.g. SEOmoz @ DomainTools & SEOmoz @ Alexa)
• SSL Certificates Issued - via DomainTools Search
• IP History - via DomainTools Search
• Hosting History - via Netcraft
• Whois History - via DomainTools Search
  (e.g. SEOmoz)

Statistics/Popularity Data

• Alexa Rank - via Alexa
  (e.g. SEOmoz @ Alexa - 864th most popular site)
• Alexa Reach - via Alexa
  (e.g. SEOmoz @ Alexa - 1395 per million users)
• Alexa Page Views Estimate - via Alexa
  (e.g. SEOmoz @ Alexa - 2.7 per user)
• Google Trends Data - via Google Trends
  (e.g. SEOmoz - no data; only available for highly searched-for domains)
• Compete Snapshot - via Compete.com
  (e.g. SEOmoz - 5854 visitors in August, ranked #204,215th most popular site; no direct linking in)
• Ranking.com Rank - via Ranking.com
  (e.g. SEOmoz - 26,741st most popular site)
• Netcraft Ranking - via Netcraft
  (e.g. SEOmoz - 20,319th most popular site)
• Bloglines Subscribers - via Bloglines Feed Search
  (e.g. SEOmoz - 448 subscribers)

Search Engine Indexing Data

• Google's Indexed Pages - via Google site: command
  (e.g. SEOmoz - 18,400 pages)
• Yahoo! Pages Indexed - via Yahoo! Site Explorer
  (e.g. SEOmoz - 5,432 pages)
• MSN Pages Indexed - via Live.com  site: command
  (e.g. SEOmoz - 11,416 pages)
• Ask.com Pages Indexed - via Ask
  (e.g. SEOmoz - 362; note that this requires an additional term in the query to return results)
• Gigablast Pages Indexed - via Gigablast Advanced Search
  (e.g. SEOmoz - 1 page)
• Exalead Pages Indexed - via Exalead
  (e.g. SEOmoz - 5,481 pages)
• Clusty Pages Indexed - via Clusty Advanced Search
  (e.g. SEOmoz - 5,867 pages)
• How this Site Looked in the Past - via Wayback Machine
  (e.g. SEOmoz - all the way back from February of 2005)

Link Data

• Yahoo! Link Data - via Yahoo! Site Explorer
  (e.g. SEOmoz - 187,234 external links)
• Technorati Link Data - via Technorati
  (e.g. SEOmoz - 8,961 links from 2,541 blogs)
• MSN Link Data - via Live.com
  (e.g. SEOmoz - 107,512 external links)
• Google Link Data - via Google (note that this information is purposefully inaccurate)
  (e.g. SEOmoz - a uselessly erroneous 2,370 links)
• Google PageRank - via RankAlert (shows for all 72 datacenters)
  (e.g. SEOmoz - PR 5/10 or 6/10 depending on DC)
• Exalead Links - via Exalead
  (e.g. SEOmoz - 4,308 external links)

Social Tagging Data

• Bookmarks at Del.icio.us - via Del.icio.us
  (e.g. SEOmoz - 31 pages, thousands of bookmarks)
• Pages in StumbleUpon - via StumbleUpon Reviews
  (e.g. SEOmoz)
• Mentions at Digg - via Digg Search
  (e.g. SEOmoz - 50+)
• Mentions at Reddit - via Reddit Search
  (e.g. SEOmoz - 21)
• Mentions at Tailrank - via Tailrank Search
  (e.g. SEOmoz - 8)
• Mentions at Newsvine - via Newsvine
  (e.g. SEOmoz - 1)

Third-Party Trust Metrics

• TrustGauge Rank - via TrustGauge
• Better Business Bureau Listings - via BBBOnline.org
• Truste Sealholders - via Truste Member List (sadly, no search function)

Important Directory & Site Listings

• Listings in the Open Directory Project - via DMOZ
  (e.g. SEOmoz - 3)
• Listings in Wikipedia - via Wikipedia Search
  (e.g. SEOmoz - 12)
• Listings in the Yahoo! Directory - via dir.yahoo.com
  (e.g. SEOmoz - 1)
• Listings in MSN's bCentral - via bCentral
• Listings in Business.com - via Google Search (as Business.com has none of their own)
• Links in Google Groups - via Groups.Google.com
  (e.g. SEOmoz - 134)

Press & Media Mentions

• Listings in Google News - via news.google.com
  (e.g. SEOmoz - 8)
• Listings in Google News Archive - via archive search
  (e.g. SEOmoz - 58)
• Listings in Yahoo! News - via news.yahoo.com
  (e.g. SEOmoz - 13)

Wow... That took a bit longer than I expected and now it's 2am... You'd think I'd learn not to start ambitious blog posts at midnight. So, dear readers, any others to share?

p.s. I almost forgot that today is the SEOmoz blog's official 2-year anniversary. Happy B-day blog :)