A lot of executive speech trainers will tell you that the biggest problem most speakers have is eye contact -- looking at a couple of friendly faces to the exclusion of everyone else, giving too much eye contact to the boss or client, or worst of all, moving back and forth from the script to the audience so much that it looks like they're watching a bungee jumper. Every good speech trainer has a bag of tricks that can fix most of these focus problems, but while their training tips may be sound, I believe the secret to successful eye contact isn't in the crowd, it's on the page.
The secret is in the proper preparation. Doesn't it make sense that if you take the time to memorize your speech and practice it enough to feel entirely comfortable, you won't have to worry about where to look. Funny, you never have trouble with eye contact when you're talking to your friends. Take that approach with your next public speaking opportunity and you'll be having a conversation with friends, not speaking off notes to a bunch of strangers.
Just think of world-class athletes like Michael Jordan, Tiger Woods, Lance Armstrong, and Mia Hamm...nobody trained harder, practiced more, or prepared more diligently, so that when it came time for competition, they were creating while everyone else was busy thinking.
If you want "full-contact" eye contact with your audience, spend more time on the page before your speech so you can spend more time off the page while you're speaking.