DazzlinDonna has a pre-made SEO contract that might be useful for those who run smaller operations and need a hand getting started in contract design. It's by no means over-arching, but it's an excellent place to start and it's free. She also has a good, basic description of the specific tasks that fit into SEO work:

(1.1). Keyword research and analysis for a maximum of (n) keywords or phrases.
(1.2). Competitive analysis for main keywords/keyphrases.
(1.3). Analysis of site architecture and linking structure.
(1.4). Analysis of HTML and page design structure.
(1.5). Recommendations for 1.1 through 1.4, above, as well as for necessary modifications to essential page text elements for achieving satisfactory search engine placement.
(1.6). Recommendations for improvement of page titles and meta tags for (n) site pages.
(1.7). Hand submission of web site to major search engines and/or directories.
(1.8). Analysis and recommendations for external links to site.