Here's what the high-traffic search engines and directory sites say influence their relevancy rankings:

Search Engine	What's not indexed	Slow Pages play a role?	Content and location	HTML Title	Meta tags	Keyword Frequency	Link popularity	What it likes
AltaVista	Registration pages, text in graphics and multimedia files (use Alt tags), XML, Java applets, comment tags, Acrobat files, spammers	Yes	Very important, Top of the page	Very important, should be unique for every page	Not important, but should be included just in case	Not mentioned, but the best location is title and top of page	Important	Uncommon words, good navigation, plain HTML pages with text only , themes, inbound links and keywords in link text.
DMOZ Users: AOL Netscape AltaVista HotBot Google Lycos	Spammers	Yes, considered poor design	Worthy of indexing as determined by editors, and in appropriate category	No, but the title filled in plays a role.	No, but the description and keywords filled in play a role.	No	Not important for DMOZ, but is Important, for some of its partners, who use Inktomi	Concise and accurate descriptions and keywords, choice of appropriate category
Google	Not mentioned, see AltaVista for approximate guidelines; spammers	Not mentioned	Keywords should be close to each other. Content should include keywords in text or links	Not mentioned, but seems to be a factor	No	Not mentioned	Very important, especially from relevant pages	Link popularity, keywords near each other, keywords in URLs and link text, themes
HotBot	Frames, pages with cookie requirements, URLs with special characters (unless submitted through Inktomi's paid program) , spammers.	Yes, pages can be dropped if a server is too slow	Ranks on the length of the document and frequency of keywords.	Most important	Very important, both description (150 characters) and keywords (75 characters)	Very important (standard requirements are 3-7%)	Important, uses Inktomi	Lack of stop words, meta tags, HTML titles, lots of keywords, link popularity, and click popularity (HotBot uses DirectHit)
Lycos	Spammers, URLs with special characters	Not mentioned	Not mentioned	Not mentioned, but seems to be a factor	Not mentioned	Not mentioned	Not mentioned, but seems to be a factor	Themes
MSN	Spammers, frames - <noframes> tag needed	No	Not mentioned	Important, should contain keywords	Both are supported; description limited to 250, keywords to 1017	Important, 4-12 times	Important, uses Inktomi	Theme present throughout the site, site popularity
Yahoo	Spammers	Yes, may be excluded	Worthy of indexing as determined by editors, and in appropriate category	No, but the title filled in plays a role. It should be concise	No, but the description and keywords filled in play a role.	No	Very important, uses Google	Concise and accurate descriptions and keywords, choice of appropriate category
Search Engine	What's not indexed	Slow Pages play a role?	Content and location	HTML Title	Meta tags	Keyword Frequency	Link popularity	What it likes