Here are some really good examples from an article written by Josh Nason on www.marketingprofs.com. His rule to remember is this: "Tell what's inside, don't sell what's inside".
From: Facebook
Subject: Pat Magoon sent you a message on Facebook...
This is about as straightforward as it gets, as I know the sender and I know the immediate reason I'm being contacted. Granted, this is an auto-responder based on a specific action, but there is no such thing as a wasted email.
From: Russell Goldstein
Subject: (none)
This was from the ESPN assistant to Le Anne Schreiber, the sports network's ombudsman. It was another auto-reply, but still... no "Thanks for the email to ESPN" or "Your ESPN comment has been received"?
From: AirTran Airways Net Escapes
Subject: 3 Days of Sale Fares for Your Much Needed Vacation!
If I've ever shopped for vacations, I'm usually going for a set location or region and not just a vague offer. Sell me a bit here, guys. Also, do we need a full four-word descriptor for the From? AirTran Airways isn't good enough?
From: Borders
Subject: 30% Coupon—Limited Time
Direct offer, simple source, timeframe established: nice work. I'd like to see "30% off everything" for future mailings to really nail it down.
From: Domino's Pizza
Subject: A Special Offer from your local Domino's Pizza
Ugh. Why so vague? Pizza chain emails traditionally are terrible and do more to deflect opens than intrigue. To date, I have never been blown away or enticed by one of these offers. Ever.
From: AAA Northern New England
Subject: AAA Newsletter—February 2008
Ah, the dreaded (Company X) Newsletter with the month and date. Fun! When I opened up the newsletter, there were all kinds of great discount offers; but, instead, this subject line reads more "library" than "block party."
From: Bob Marley
Subject: Comedian Bob Marley Returns To Boston!!
It's a direct statement that his fans in that area would likely open. Since "Bob Marley" is already in the From line, there's no need to repeat in the subject line. I'd try "Boston dates coming up soon!" instead. Why waste the valuable real estate?