Writing good title tags is an art that SEO’s perfect over time. Expert title tag writers can charge premium rates for their service and are in high demand. Merely having perfect title tags on a site can mean the difference between position 1 and position 51.
Its best to write in complete sentences or phrases. It must be readable text that a human would easily be able to understand. Use a subject + object + verb style. Place the most important words at the beginning, since people read from left to right. The page title does not need to be a complete sentence and should have minimal punctuation and no period.
Clearly state your topic and use words a user can understand. As an example, if you’re a scientist talking about “paleoclimates in the pleistocene epoch”, use more common terms such as “past global climate change”.
A good way to write a compelling title is to think of Jeopardy, and provide the question to an answer. The answer and explanation is the body content of the page, and the title tag needs to be the welcome message that introduces the topic and leads a user/spider into the content.
Keep your titles short. As Strunk & White would demand, brevity is rewarded. Omit needless words and grammar articles. Search engines ignore these anyway: a, the, and, with, at. The more words you use, the more the keywords will be diluted. Titles above 60 characters are cutoff in Search Engine Results Pages, and merely clutter the browser window chrome.
You have 3 audiences: human users, search engines, and social sites such as digg.com. I do not recommend page cloaking to present different title tags to each group. Instead take a balanced approach and write something you would want to click on yourself. If you can see your title being interesting and relevant in 10 years, it’s likely a winner.