My fav (so far) is "need a ______ in (city)" or "looking for a _____", etc.
Just gets their attention so as not to lose potential clients/cusotmers so they open the email. Nothing new here , but it still works.
As for the offer I like to keep it real short and to the point. It is better to make it look like you just typed an email to them, not just copied and pasted a long drawn out dissertation.
If I get some contributions to this thread I will give the exact email and offer that gets me good leads. It is not magical, just a foot in the door but works nonetheless.