It's worth noting that the Yurbuds you tried, while in-ear type, are not noise blocking type. In order to be noise canceling (mechanically), they need to block the canal, such as the type Dunbar posted. Whether foam or silicone, they need to fit snugly in the canal; most headsets come with multiple sizes of earpieces for this reason.

There are also active noise canceling headphones, i.e. that operate electronically to defeat ambient noise, but whether those would work on a bike, I don't know. I'd imagine that the sensing microphone would need to be positioned out of head-on wind, but I'm not sure. They may be worth playing with, but I think canal blocking earpieces would do the trick.

Wilbur has, I think, the best idea, which is to smooth airflow across the ear. The Slipstreamz "The Slip" ear covers are similar, but ready made and integrate with earbuds, so it's an easy solution. http://www.slipstreamz.com/content.asp?subID=8