How can I improve my site ranking on Google/etc? (SEO)?

[Jack B]

I am trying to get my friends anime site listed higher in the Google/Yahoo/etc results for search phrases relating to my site. The site is gurrenlagannepisodes.com, yet searching for "Gurren Lagann Episodes" doesn't list it until like page 9.

We've already done a lot of things, including:
-The site contains plenty of relevant content
-It has relevant metatags, keywords, title, etc
-URLs are search engine friendly
-We have a sitemap
-We have a robots.txt
-We post the site on other sites (linkbacks)