The cover picture should have the betdog logo in it (final_logo.ai) and the slogan "Track your bets". The top one is the main color template. You can use one of the other color options if it fits better with your design/colors.
It's a pretty boring looking website (see the layout on overview.jpg and bet_slip.jpg), so it's not much you can take from that to spice up the coverphoto. The only thing you poissibly could use is the graphs and charts (see netprofit.jpg and sports.jpg). An alternative could be to have screenshots from the website.
Take a look at the website at http://www.fjoller.com using the login info above. The pre-login frontpage is still under construction (see starter_page_slideshow.pdf for new layout).
One suggestion you could try out is something like this: http://www.dreamgrow.com/23-cool-ex (#14. ExactTarget)
Replacing the ExactTarget logo with the betdog logo and the slogan "Track your bets". What an alternative to that picture would be I don't know. Considering it is a site for sports bettors, something sports related could be an alternative. OR maybe some graphs.
If you want to, you can make changes to the profile picture (fbprofile.ai) to combine the profile photo and cover photo (like this http://www.facebook.com/CarMax). Please inlcude the profile picture in your sample.