I've been around since 1998 and it's definitely not as easy as it used to be. But there's STILL plenty of money to be made. As has been pointed out you just need to think outside the box, innovate and not stay stagnant.
One great way to find out what's selling it to take advantage of all the promo payouts everyone is having. Every program out there has $100 days. Make a schedule and promote each of those and I'm sure you're going to come across a great seller for your traffic.
Take our promo for example: Hotbox.com. We're paying $150 per sale this entire MONTH!
At $150 per sale you can't go wrong
Anyone promoting us is welcome to hit me up for some pointers.