There's a great roundup of the factors, and how important they are thought to be, at SEOMoz
http://www.seomoz.org/article/search-ranking-factors#ranking-factors
On-Page (Keyword-Specific) Ranking Factors
- Keyword Use Anywhere in the Title Tag
- Keyword Use as the First Word(s) of the Title Tag
- Keyword Use in the Root Domain Name (e.g. keyword.com)
- Keyword Use Anywhere in the H1 Headline Tag
- Keyword Use in Internal Link Anchor Text on the Page
- Keyword Use in External Link Anchor Text on the Page
- Keyword Use as the First Word(s) in the H1 Tag
- Keyword Use in the First 50-100 Words in HTML on the Page
- Keyword Use in the Subdomain Name (e.g. keyword.seomoz.org)
- Keyword Use in the Page Name URL (e.g. seomoz.org/folder/keyword.html)
- Keyword Use in the Page Folder URL (e.g. seomoz.org/keyword/page.html)
- Keyword Use in other Headline Tags ( – )
- Keyword Use in Image Alt Text
- Keyword Use / Number of Repetitions in the HTML Text on the Page
- Keyword Use in Image Names Included on the Page (e.g. keyword.jpg)
- Keyword Use in or Tags
- Keyword Density Formula (# of Keyword Uses ÷ Total # of Terms on the Page)
- Keyword Use in List Items
- on the Page
- Keyword Use in the Page’s Query Parameters (e.g. seomoz.org/page.html?keyword)
- Keyword Use in or Tags
- Keyword Use in the Meta Description Tag
- Keyword Use in the Page’s File Extension (e.g. seomoz.org/page.keyword)
- Keyword Use in Comment Tags in the HTML
- Keyword Use in the Meta Keywords Tag
On-Page (Non-Keyword) Ranking Factors
- Existence of Substantive, Unique Content on the Page
- Recency (freshness) of Page Creation
- Use of Links on the Page that Point to Other URLs on this Domain
- Historical Content Changes (how often the page content has been updated)
- Use of External-Pointing Links on the Page
- Query Parameters in the URL vs. Static URL Format
- Ratio of Code to Text in HTML
- Existence of a Meta Description Tag
- HTML Validation to W3C Standards
- Use of Flash Elements (or other plug-in content)
- Use of Advertising on the Page
- Use of Google AdSense (specifically) on the Page
Page-Specific Link Popularity Ranking Factors
- Keyword-Focused Anchor Text from External Links
- External Link Popularity (quantity/quality of external links)
- Diversity of Link Sources (links from many unique root domains)
- Page-Specific TrustRank (whether the individual page has earned links from trusted sources)
- Iterative Algorithm-Based, Global Link Popularity (PageRank)
- Topic-Specificity/Focus of External Link Sources (whether external links to this page come from topically relevant pages/sites)
- Keyword-Focused Anchor Text from Internal Links
- Location in Information Architecture of the Site (where the page sits in relation to the site’s structural hierarchy)
- Internal Link Popularity (counting only links from other pages on the root domain)
- Quantity & Quality of Nofollowed Links to the Page
- Percent of Followed vs. Nofollowed Links that Point to the Page
