Although not a perfect test, carotid ultrasound is an exceptionally easy and accessible test. Using high-frequency sound, clear images are available for most people.
I say it's not perfect because the way it's done in 2006 makes it a non-quantitative test. It is a qualitative test. In other words, you may find out that there's a 30% blockage ("stenosis"), at the far end of the common carotid artery on the right side. Unfortunately, this gives you an isolated measure of diameter of the plaque compared to the artery. What it does not tell you is what the volume of the entire plaque is. That's a far more accurate measure (and one that is incorporated into your heart scan score, by the way).
Nonetheless, carotid ultrasound is easy, very safe, and available in most hospitals and many clinics. One difficulty: most insurance companies will not allow you to go through a carotid ultrasound scan as a "screening" procedure, i.e., a test just to see if you have a carotid plaque. They will generally pay if you're having symptoms of a stroke or "mini-stroke" (transient ischemic attack, or "TIA"), have an abnormal sound in your carotid ultrasound detected by your doctor (a carotid "bruit"), or some other unusual indications. Sometimes, a resourceful physician will muster up a diagnosis based on something in your history (e.g., left arm numbness, a common and often benign complaint that can also signal stroke).
Another option are the mobile scanners or some hospital services that offer carotid screening, usually for a very modest price. Drawback: Sporadic availability, difficulty in obtaining serial scans, and imprecise reporting since it's viewed as a screening test. But it's better than nothing.
My hope is that, as screening services using safe imaging techniques like ultrasound propagate and increase in direct availability to the public, you'll be able to circumvent the obstacles imposed by your insurance company and even, sometimes, your doctor. But try your doctor first.