You can add some real value to your site by adding links to dictionary sites. This is especially useful if you have pages with new terminology or difficult words. A nice service is Dictionary.Com,...
Search Engines Vs Usability
Sometimes people seem to make a choice between making their site pretty for search engines or making it useful for people. I am always fascinated when I hear this discussion. In fact, it is interesting to hear someone say "I'm removing my Webring because Google will get annoyed" or "I'm deleting my links page because god, uh, Google, won't like it", or "search engines don't use meta tags, so I took them all out". These comments all ignore the basic datum about the internet. It's about PEOPLE! The internet is not about some silly, stupid little robots, or some faceless idiotic rules enforced by their creators. The internet is about communication.
Yes, search engines are a part of that communication, as it is one (and only ONE) want of getting people to your site. But there are an infinite number of other ways to get people to your site, from viral marketing to Webrings to link exchanges to contests to newsgroups to whatever else you can think of.
But if your site does not cater to PEOPLE, it will fail. Period.
Yes, it's a good idea to make sure your site is known to the engines and known well. But that is NOT the purpose of the site. The purpose of the site is to communicate. Pure and simple.
Google's customers are advertisers; the searchers are the commodity that's being sold to the advertisers. The search engine is the bait used to get the commodity to view the advertisements. SEO types tend to reduce the value of the bait, which in turn lowers the value of the commodity, which in turn makes the advertisers (the customers) more likely to look elsewhere.