The helpful team at Mailchimp have provided some examples from their huge dataset of email subjects lines that worked really well at enticing people to read emails and some which bombed.
Note how clever-clever in-your-face electronic equivalent of charity chugging doesn’t usually work well:

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RT @markpack: New from me: Best email subject lines – http://bit.ly/e44Fy0
[...] Subject lines matter: the subject line on an email is rather like the headline on a Focus leaflet - it needs to give people an instant reason to read on and should get over your key message so that they get it even if they hit delete rather than reading on. As a result, often the most effective subject lines therefore are short, clear and factual. [...]