I was astonished to find that the more-than plentiful sales and/or marketing emails, which I would usually only read the subject line without actually opening the email, then I would delete it unread, were extremely fruitful.
I found 'hidden' competitions further into the body of the email - obviously designed to make us open and read them. It's worked - In two days I found 27 competitions I would normally have deleted without even knowing the comp was there.
Here are some examples:
From: Bayliss and Harding
Subject: Bank Holiday Treat - FREE POSTAGE until Tuesday
1/2 way down: Win a luxury holiday
Subject: Back to school
Very bottom of email: 2 x competitions - London Break / School items
From: The Lady
Subject: The Countdown to Downtown
1/2 way down: Win a coat plus link to 8 x comps on website
From: The Frangrance Club
Subject: Bank Holiday Weekend - 70% off
Bottom of email: Win Lady Gaga perfume
From: Hot Diamonds
Subject: New Charms from Hot Diamonds! Preview our 'Diamond Moments' collection now!
1/2 way down: Win a silver pendant
Subject: Imogen Thomas' mum-2-be blog; back to school health Qs; how to get ready for birth
bottom of email: 3 x comps for a holiday/£50 shopping vchr/birthing device (OK this last one I'm not entering!!!)
Some of the sites I already look out for, as I expect you do, because you know there are comps on the site. Others I have never been on their site before and I wonder how many comps I have "thrown away"!
It takes much, much longer to clear your inbox - but well worth it if you want to pick up a few extra comps.
As I find these I am trying to 'share' everything I can. It's a tough job but I've got a lot of Karma to use up :)
Good Luck all